MHC Antigens and NK Cells Immunol Res 1992;11:133-140
JosOPe~a Rafael Solana ImmunologyUnit, Department of Biochemistry,Schoolof Medicine, Reina SofiaHospital, Universityof C6rdoba, Spain
9 . , * * Q . . ~ 1 7 6 1 7 6 1 7 6 1 7 6 ~ 1 7 6 1 7 6 1 7 6 1 7 6
Key Words Natural killer MHC class I antigen Cell lysis yIFN Transfection
Histocompatibility Antigens and Natural Killer Susceptibility I J e l o l o o o o o o o * o l o l o l t a o t . o l o o o o o l o . a t . o * ~ 1 7 6
J o o o * l * * J * o * o ~
Abstract The central question of the nature of the structure(s) involved in the recognition of targets by natural killer (NK) cells remains unresolved. Although NK-mediated cytotoxicity is not MHC-restricted, it has been suggested that these cells could recognize the targets more effectively in the absence of MHC class I antigens. In this paper we review the contradictory results obtained when studying the NK susceptibility of cell lines which constitutively express different levels of MHC antigens, or which have been induced to express MHC antigens by gene transfection or gamma-interferon treatment. Taken together, the results indicate that MHC antigens play a differential role in NK lysis depending on the nature of the target cells used; MHC class I antigens play a role in the NK resistance of cells from a hematopoietic lineage, but this does not extend to cells from other origins. The data reviewed also support the hypothesis that MHC class t antigens induced NK resistance by interfering with target structures, and that multiple NK molecules are involved in NK-mediated lysis as part of a possible advanced recognition system. * * 4 * o * ~
Introduction It is well known that natural killer (NK) cytotoxicity is involved in a wide series of defensive immunological functions. NK-mediated lysis implies previous recognition and binding of target and effector cells. Although different molecules have been reported to play a role in the interaction between these cells, their precise nature and function have not yet been clearly defined [ 1-4]. Contrary to
what occurs with the T lymphocytes which recognize antigens only when they are presented in association with major histocompatibility (MHC) antigens, NK-mediated lysis is not restricted by the histocompatibility products. Moreover, it has been suggested that MHC class I antigen expression on target cells reduces their susceptibility to be lysed. This hypothesis has stimulated a great deal of interest and controversy due to the conflicting results found by different authors in a
Prof. J. Pefia Department of Biochemistry School of Medicine Av. Men~ndez Pidal, s/n E-14004 C6rdoba (Spain)
9 1992 S. Karger AG, Basel 0257-277X/92/ 0112-013352.75/0
Table 1. Effect of increased MHC class I antigen expression on NK susceptibility of target cells from different origins
Model
Cell type
NK sensitivity
References
Murine Murine Murine Human Human Human Human Human
lymphoma (EL4, RBL5) lymphoma (YAC 1) fibrosarcoma (GR9 clones) tymphoblastoid (HBS, HMy2) EBV cell lines (721 mut.) EBV cell lines (MM-1 mut.) solid tumor cell lines solid tumor cell lines
block block block block block block no effect no effect
5, 19 7 8 10 i1 12 14 15-17
variety of experimental models. Thus, the susceptibility of tumor cells with different levels of MHC antigens to lysis by NK cells has been extensively studied. From a general point of view three particular experimental conditions have been used: (a)NK lysis of target cells expressing different levels of MHC antigens, (b) the effect of MHC gene transfection of target cells on NK susceptibility, and (c)the effect of gamma-interferon (yIFN) treatment on target MHC antigen expression and NK susceptibility. In this paper, the results obtained from these studies are reviewed and analyzed in order to evaluate the role that the MHC class I antigens on the target cells play in NK cell recognition and lysis.
NK Susceptibility of Cells Expressing Different Levels of MHC Antigens NK susceptibility of tumor cells with different levels of MHC class I antigens is heterogeneous (table 1). The initial observations, both in vivo and in vitro, demonstrating a relationship between decreased NK sensitivity and increased H-2 expression in variants of several murine lymphomas (YAC-1, RBL5, EL4) [5-7] gave rise to the hypothesis that one function of N K cells is to lyse cells that fail to express MHC antigens (missing-selfhypothe-
134
Pefia/Solana
sis). Thus, NK cells could be acting as a defensive system complementary to the recognition and elimination of target cells by Tc lymphocytes, where Tc cells would kill cells expressing self MHC class I antigens associated with altered or foreign peptides, and NK cells those with reduced MHC class I antigen expression. The missing-self hypothesis proposes that low levels of MHC antigens may confer susceptibility to NK lysis. A similar relationship between low expression of MHC class I antigens and NK susceptibility was obtained in clones from a murine fibrosarcoma [8], and B16 melanoma cells pretreated with yIFN and inoculated intravenously [9]. Using a panel of human cell lines derived from T lymphoblastoid cells and from a lymphoma B cell line (HMy2), Storkus et al. [10] found that NK susceptibility varied inversely with the level of target cell class I HLA antigen expression. This correlation has also been observed in other human EBV transformed B cell lines [ 11, 12]. However, these results cannot be extended to other types of tumors, as different studies show that HLA antigen expression has no effect on NK susceptibility when human cell lines derived from lung carcinomas [13], sarcoma or melanoma [ 14] are used. Our results (table 2) with cell lines derived from solid tumors also suggest that N K susceptibility is
MHC and NK Activity
Table 2. M H C expression and N K resistance of cell lines obtained from primary and metastatic brain tumors N K sensitivity + MHC + MHC -
4 6
6 5
Values represent the number of cases. Adapted from references 16 and 17.
independent of the level of HLA class I expression [ 15-17]. Cell lines expressing high levels of HLA antigens can be either NK resistant or NK susceptible, and those expressing nondetectable levels can also be resistant or susceptible to NK cytotoxicity. One possible explanation for the discrepancy in the results obtained by different investigators could be related to the nature of the different tumors used. Thus, when target cells from hematopoietic origin were analyzed, a significant effect of the MHC class I products on the susceptibility of the target cell to be lysed by NK cells was generally found. However, in studies with cell lines from solid tumors, no relationship between MHC class I expression and NK susceptibility was observed, indicating that target cell properties, other than the lack of MHC class I antigens, affect target cell sensitivity to NK lysis. In fact, NK cells interact with target cells through several surface molecules and their corresponding ligands [3, 18-20]. This can explain the contradictory results as these structures could be differentially expressed on tumor cells of different origin. This possibility has also been proposed by Ljunggrenn and Karre [ 19] who reinterpret the contradictory results in the literature within a multiple-
choice model. This model proposes that N K cells use different mechanisms for target recognition and lysis, and that one of these mechanisms is affected by MHC class I antigen expression. Two other nonexclusive interpretations can be given: (1) that MHC Ag expression and NK target structures are concurrently regulated in some but not all target cells (probably depending on the specific cell lineage or the factor(s) involved in malignant transformation), and (2)that MHC Ag are physically associated with NK target structures in certain target cells, blocking their recognition by the NK effectors (although depending on the cells, the target structures can be differentially expressed).
NK Susceptibility of Cells Transfected with MHC Class I Genes
The possibility of transfecting MHC genes into MHC-negative target cells has provided the opportunity to directly study whether or not MHC class I products affect NK susceptibility. Target susceptibility before and after transfection with MHC class I genes has been studied in both murine and human models. The results obtained (table 3), depend once again, on the target cells used. In murine models, transfection of H-2K b genes in hepatoma cells [21] and H-2Dp genes in lung carcinomas [22] has no direct effect on N K resistance. On the other hand, transfection of H-2 genes to an MHC-deficient murine lymphoma variant [23] and to a melanoma cell line [24] makes them resistant to NK lysis. When human target cells are considered, the results found by different authors demonstrate that whereas transfection of HLA class I or 13-2microglobulin genes induces resistance to NK lysis when EBV-transformed cell lines are used [25-28], HLA class I gene transfection does not significantly affect NK suscepti-
135
Table 3. Effect of MHC class I gene transfection on NK susceptibility of target ceils Model
Cell type
Transfecting genes
NK sensitivity
Reference
Murine Murine Murine Human Human Human Human Human Human
hepatoma (BW7756) lung carcinoma EL-4 mutant lung carcinoma (GLC2) lymphoma (DAUDI) lymphoblastoid (HMy2) lymphoblastoid (HMy2) lymphoblastoid (HMy2) cell lines (K 562, MOLT4)
H-2K b H-2DP
no effect no effect decreases no effect decreases decreases decreases decreases no effect
21 22 23 13 25 26 27 28 29
HLA class 1/132micro, 132 microglob, HLA class I ct1/ct2 domains HLA class I HLA class I
bility of target cells from other origins such as human lung carcinoma [13] or the classical NK targets, K562 or Molt4 [29]. Furthermore, it has been recently shown [30] that a single amino acid in the peptide binding groove of HLA can be responsible for the protective effect of NK lysis. In short, the results obtained from target cells transfected with MHC class I genes are not conclusive, the induction of resistance depending on the target cell used. The fact that transfection does not affect NK susceptibility when MHC gene products are transfected into cell lines of nonhematopoietic origin such as lung carcinoma [22] or hepatoma [21] in mouse, and human lung carcinoma [ 13], and that HLA class I antigens play a critical role in NK resistance in human cell lines transformed by EB virus [25-28] is of interest. It supports the view that MHC antigens play a differential role in NK recognition and lysis depending on the cells used as targets, and suggests that in some cell lines MHC class I antigens interact with the NK target structures blocking their recognition by effector cells. However, this model cannot be extended to all NK-susceptible target cells, corroborating the assumption that different mechanisms for target cell recognition and lysis are involved in NK cell activity.
136
Pefia/Solana
NK Susceptibility and MHC Levels in yIFN-Treated Cells IFN is being extensively used in therapy with contradictory results, and so its biological properties need to be further studied. It has been shown that 7IFN induces HLA molecule expression on a wide range of tumor cells [31], and it is generally agreed that treatment of NK-susceptible target cells with IFN results in a decreased susceptibility to lysis by NK cells [21, 24, 31-36]. The mechanism involved in NK resistance by 7IFN treatment are not fully understood [3, 17, 37-41], although it has been suggested that the changes in MHC antigen expression induced by this lymphokine could be responsible for NK blocking recognition and lysis [5, 23, 24] (table 4). In murine lymphomas or human K562 treated with 7IFN, a decreased N K susceptibility and increased HLA class I antigen expression were observed. However, IFN treatment can induce NK resistance without modifying MHC class I antigen expression in brain tumor cell lines [I 5, 17], sarcomas [14] and hepatomas [21]. Notwithstanding, the possible role of MHC antigens induced by 7IFN in resistance to NK lysis is difficult to evaluate. An example of these difficulties arises in two reports in which similar experi-
MHC and NK Activity
Table 4. NK susceptibility and MHC class I expression in 7IFNtreated target cells
Model
Cell type
MHC in- NK duction sensitivity
Reference
Murine Murine Murine
YAC- 1 BL-6 EL-4 EL-4 mutant lymphoma (RAJI) sarcoma ($4) melanoma (M 14) EBV transfected solid tumors K562 lung carcinoma (GLC2)
yes yes yes no no
decreases decreases decreases no effect decreases
7 24 23
no no yes yes
no effect decreases decreases decreases
12 17
Human
Human Human Human
mental approaches come to opposite conclusions: while K562 cells become NK resistant with yIFN treatment and not with HLA class I gene transfection [28, 42], murine EL4 variants become resistant to NK lysis with H-2 gene transfection but not with 7IFN treatment [23]. These data demonstrate once more that MHC expression cannot be used to explain 7IFN-mediated NK resistance in all cell lines. Moreover, in a more recent study we found that a non MHC-related structure, a tumor factor produced by the CAP-2 cell line (NK-RIF), also induces NK resistance without inducing MHC class I antigens [43-45]. In an attempt to further clarify how MHC antigens could participate in 7IFN-induced NK resistance, the different stages o f N K lysis have also been studied. NK lysis is the result of a multiple-step process in which the different stages involved in resistance need to be evaluated. Initially, NK effector ceils bind targets via an appropriate structure, forming conjugates [3, 4, 18, 36, 46-48]. After recognition, NK effector cells trigger or program lysis and release the cytolytic factor(s) (NKCF). Finally, NKCF irreversibly binds to the target cells leading to cell death.
14
13
In some of these studies, no relationship between conjugate formation and MHC antigen expression has been observed (e.g. in IFNtreated K562) [38, 42], indicating that the induction of NK resistance by MHC Ag is a post-binding event as represented in figure I. On the other hand, Storkus et al. [10] found such a correlation in a panel of human cell lines. In one of our studies on the NK lyric process using 7IFN-treated K562 and separated into HLA-positive an HLA-negative subsets, we observed that both populations formed a similar number of target-effector conjugates, although the HLA-positive population had a reduced capacity to trigger NK cell activation [42].
Conclusions
The results reviewed demonstrate that target MHC class I antigens play a clear role in NK resistance of murine lymphomas and melanomas and human EBV-transformed Bcell lines. Results also show that it is not possible to extend this function to cell lines of different origins, indicating that MHC antigens react differently to NK lysis depending on the
137
T a b l e 5. MHC expression and NK resistance in tumors of different nature
NK LYSIS
Cell line origin
TARGET
EFFECTOR )
MHC effect on NK lysis
Hematopoietic leukemias Solid tumors
block
no block
16 4
2 5
CELL
CELL
Values represent the number of reports using different experimental approaches.
O 9
i•loOoO0
NKCF
target ceils used (table 5). These findings support the hypothesis that multiple target structures are involved in NK-mediated lysis. In experimental models such as 7IFN-treated K562 ceils, the relationship between M H C antigens and N K resistance may be more a consequence o f a coordinate expression of both the N K target structure and the M H C products than o f a direct effect of the antigens. Furthermore, in those cases in which M H C is involved, the results suggest that they are probably interfering with target structures instead o f inducing an inhibitory signal for N K cells, as it is possible to render NK-sensi-
138
Pefia/Solana
Fig. 1. NK lysis is the result ofa multistep process, which starts with the recognition and binding of the target (first step). The effector adhesion molecules LFA-I (CD1 la/CD18) or CD2 bind to target structures ICAM-1 (CD54) or LFA-3 (CD58), respectively. Other NK-specific molecules are probably participating in the effector-target conjugate formation. This is followed by the NK effector triggering (second step) which involves hydrolysis of phosphatidyl-inositol, activation of protein kinase C, and Ca~-+mobilization. With the subsequent release of NKCF, and finally the binding of the NKCF to the target cell, cell death results (third step). MHC antigens could participate in some experimental models by interfering with the postbinding activation of the effector cells and blocking NK activation and the secretion of NKCF.
tive target cells resistant to N K lysis despite reduced M H C expression. Thus, further studies to determine the exact mechanisms o f N K lysis o f target ceils from different origins are necessary, especially as it has recently been suggested [46] that N K cells possess an advanced recognition system.
Acknowledgements The authors thank Ms. Christine Mendez and Ms. M.L. Velarde for their collaboration in the preparation of the manuscript. This work was supported by grants from the CICYT and FIS (Spain).
MHC and NK Activity
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References 1 Chambers WH, Vujanovic LN, De Leo AB, Olszowy MW, Herberman RB, Hiserodt JC: Monoclonal antibody to a triggering structure expressed on rat natural killer cells and adherent lymphokine- activated killer cells. J Exp Med 1989;169: 1373-1383. 2 Harris DT, Jaso-Friedmann L, Devlin RB, Koren HS, Evans SL: Identification of a human natural killer cell target cell antigen with monoclonal antibodies. J Immunol 1989; 143:727-735. 3 Trinchieri G: Biology of natural killer cells. Adv Immunol 1989;47: 187-342. 4 Ortaldo JR, Hiserodt JC: Mechanisms of target cell killing by natural killer cells. Curr Opin lmmunol 1990: 2: 39-44. 5 Karre K, Ljunggren JH: Piontek G, Kiessling F: Selective rejection of H2 deficient lymphoma variants suggests alternative immune defense strategy. Nature 1986;319:675-678. 6 Karre K: Role of target histocompatibility antigens in regulation of natural killer activity: A reevaluation and a hypothesis, in Herberman RB, Callewaert D (eds): Mechanisms of Cytotoxicity by Natural Killer cells. Orlando, Academic Press, 1985, pp 81-85. 7 Piontek GE, Taniguchi K, Ljunggren H, Gronberg A, Kiessling R, Klein G, Karre K: YAC-I MHC class I variants reveal an association between decreased NK sensitivity and increased H-2 expression after interferon treatment or in vivo passage. J Immunol 1985;135:42814288. 8 Algarra I, Ohlen C, Perez M, Ljiinggren HG, Klein G, Garrido F, Karre K: MHC class I deficient cells within a heterogeneous fibrosarcoma show elevated NK sensitivity and reduced survival in the lungs after intravenous administration. Int J Cancer 1989;44:675-680.
9 Taniguchi K, Petersson M, Hoglund P, Kiessling R, Klein G, Karre K: Interferon 7 induces lung colonization by intravenously inoculated B 16 melanoma ceils in parallel with enhanced expression of class I mayor histocompatibility complex antigens. Proc Natl Acad Sci (USA) 1987;84: 3405-3409. 10 Storkus WJ, Howell DN, Salter RD, Dawson JR, Cresswell P: NK susceptibility varies inversely with target cell class I HLA expression. J Immuno11987;138:1657-1659. l I Harel-Bellan A, Quillet A, Marchiol C, Demars R, Tursz T, Fradelizi D: Natural killer susceptibility of human cells may be regulated by genes in the HLA region of chromosome 6. Proc Natl Acad Sci (USA) 1986;8: 5688-5692. 12 Ohl~n C, Bejarano MT, Grrnberg A, Torsteinsdottir, S, Fransksson L, Ljunggren HG, Klein E, Klein G, K/irre K: Studies ofsublines selected for loss of HLA expression from an EBV-transformed lymphoblastoid cell line: Changes in sensitivity to cytotoxie T cells activated by allostimulation and natural killer cells activated by IFN or IL-2. J lmmunol 1989;142:3336-3341. 13 Stam N J, Kast WM, Voordouw AC, Pastoors LB, Van der Hoeven FA, Melief CJM, Ploegh IlL: Lack of correlation between levels of MHC class I antigen and susceptibility to lysis of small cellular lung carcinoma by natural killer cells. J Immuno11989;142:4113-4117. 14 de Fries R, Golub SH: Interferon reduces the sensitivity of cultured and fresh human tumor cells to lysis by lymphokine-activated killer cells. Nat Immun Cell Growth Regul 1988;7:65-76. 15 Alonso C, Serrano R, Solana R, Pefia J: Natural killer susceptibility of brain tumor cell lines inversely correlates with the degree of cell differentiation. Int Arch Allergy Appl Immunol 1989;89:169-172. 16 Pefia J, Solana R, Alonso C, Santamar/a M, Serrano R, Ramirez R, Carracedo J: MHC class I expression on human tumor cells and their susceptibility to NK lysis. J Immunogenet 1989; 16:407-412.
17 Pefia J, Alonso C, Solana R, Serrano R, Carracedo J, Ramirez R: Natural killer susceptibility is independent of HLA class I antigen expression on cell lines obtained from human solid tumors. Eur J Immunol 1990;20: 2445-2449. 18 Lotzova E, Ades EW: Natural immune killer cells definition, heterogeneity, lytic mechanism, genetics and clinical application. Highlights of the fifth international workshop on NK cells. Nat Immun Cell Growth Regul 1989;8:1-7. 19 Ljunggren HG, Karre K: In search of the 'missing self: MHC molecules and NK cells recognition. Immunol Today 1990;11:237-244. 20 Solana R, Serrano R, Pefia J: MHC antigens in NK recognition and lysis. lmmunol Today 1991 ;12:95. 21 Nishimura M, Stroynowski I, Hodd L, Ostrand-Rosenberg S: H-2K b antigen expression has no effect on natural killer susceptibility and tumorigenicity o f a murine hepatoma. J Immunol 1988;141:4403-4409. 22 Dennert G, Landou C, Lord EM, Bahler DW, Frelinger JK: Lysis of a lung carcinoma by poly I-C-induced natural killer cells is independent of the expression of class I histocompatibility antigens. J lmmunol 1988: 140:2472-2475. 23 Sturmhofel K, Hammerling G: Reconstitution of H-2 class I expression by gene transfection decreases susceptibility to natural killer cells of an EL4 class I loss variant. Eur J Immunol 1990;20:171-175. 24 Gorelik E, Gunji Y, Herberman R: H-2 antigen expression and sensitivity of BL6 melanoma cells to natural killer cell cytotoxicity. J Immunol 1988; 140:2096-2101. 25 Quillet A, Presse F, Marchiol-Fournigault C, Harel-Bellan A, Benbunan M, Ploegh H, Fradelizi D: Increased resistance to non-MHC-restricted cytotoxicity related to HLA A, B expression. Direct demonstration using ~2-microglobulin transfected Daudi cells. J Immunol 1988; 141:17-20.
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26 Storkus W J, Alexander J, Payne JA, CressweU P, Dawson JR: The ctl Rt2 domains of class I HLA molecules confer resistance to natural killing. J Immuno11989;143:3853-3857. 27 Storkus WJ, Alexander J, Payne AJ, Dawson JR, Cresswell P: Reversal of natural kilIing susceptibility in target ceils expressing transfected HLA class I genes. Proc Natl Acad Sci (USA) 1989;86:2361-2364. 28 Sbimizu Y, Demurs R: Demonstration by class I gene transfer that reduced susceptibility of human cells to natural killer cell-mediated lysis is inversely correlated with HLA class I antigen expression. Eur J Immuno11989;19:447-451. 29 Leiden JM, Kornbluth J: Susceptibility to natural killer cell mediated cytolysis is independent of the level of target cell class I HLA expression; in Ades EW, Lopez C (eds): Natural Killer Cells and Host Defense. 5th Int NK Cells Workshop. Basel, Karger, pp 198-206. 30 Storkus WJ, Salter RD, Alexander J, Ward FE, Ruiz RE, Creswell P, Dawson JR: Class I induced resistance to natural killing: Identification of nonpermissive residues in HLA-A2. Proc Natl Acad Sci (USA) 1991 ;88:5989-5992. 31 Woodroofe MN, Hayes GM, Cuzner L: Fc receptor density, MHC antigen expression and superoxide production are increased in interferon gamma treated microglia isolated from adult rat brain. Immunology 1989;68:421-425. 32 Giuliani-Bonmassar A, Graziani L, Frati L, Bonmassar E: Interferoninduced changes in the susceptibility of murine and human lymphoma cells to natural cytotoxic lymphocytes, lnt J Tissue React 1984;6:3542. 33 Moore W, White M, Potter MR: Modulation of target cell susceptibility to human natural killer cells by interferon. Int J Cancer 1980;25: 565-570.
34 Trinchieri G, Santoli D: Antiviral activity induced by culturing lymphocytes with tumor-derived or vires-transformed cells. Enhancement of human natural killer cell activity by interferon and antagonistic inhibition of susceptiblity of target ceils to lysis. J Exp Med 1978;147:13t41321. 35 Welsh RM, Karre K, Hansson M, Kunker LA, Kiessling RW: Interferon-mediated protection of normal and tumor target cells against lysis by mouse natural killer cells. J Immunol 1981;126:219-224. 36 Witte T, Wordelmann K, Schmidt RE: Heterogeneity of human natural killer cells in the spleen. Immunology 1990;69:166-172. 37 Gronberg A, Kiessling R, Masucci G, Guevara LA, Eriksson E, Klein G: Gamma-IFN (IFN-'/) produced during effector and target interactions renders target ceils less susceptible to NK-cell-mediated lysis, lnt J Cancer 1983;32:609-615. 38 Gronberg A, Ferm MT, Reynolds CW, Ortaldo JR: IFN-gamma treatment of K562 cells inhibits natural killer cell triggering and decreases the susceptibility to lysis by cytoplasmic granules from large granular lymphocytes. J Immunol 1988;14: 4397-4402. 39 Powell J, Stone J, Chan VC, Yang Z, Leatherbury A, Sell KW, WiktorJedrzejczak W, Ahmed-Ansari A: Interferon-gamma-treated K562 target cells distinguish functional NK cells from lymphokine-activated killer (LAK) cells. Cell Immuno11989;118:250-259. 40 Uchida A, Vanky F, Klein E: Natural cytotoxicity of human blood lymphocytes and monocytes and their cytotoxic factors: Effect of interferon in target cell susceptibility. J Natl Cancer Inst 1985;75:849854.
41 Wright SC, Bonavida B: Studies on the mechanism of natural killer cellmediated cytotoxicity. IV. Interferon induced inhibition of NK target cell susceptibility to lysis is due to a defect in their ability to stimulate release of natural killer cytotoxic factors (NKCF). J lmmunol 1983; 130:2965-2972. 42 Ramirez R, Solana R, Carracedo J, Alonso MC, Pefia J: Mechanisms involved in NK resistance induced by interferon-'/. Cell Immunol 1992; 140:248-256. 43 Serrano R, Alonso C, Solana R, Monserrat J, Mufioz J, Pefia J: Identification of a tumor factor inducing resistance to NK cell lysis. Immunol Lett 1989;20:311-316. 44 Solana R, Alonso C, Ramirez R, Carracedo J, Serrano R, Yiangou Y, Pefia J: Analysis of the mechanisms involved in NK resistance induced by a new tumor factor NK-RIF. Cell lmmunol 1990;130:244-251. 45 Serrano R, Yiangou Y, Solana R, Sachs JA, Pefia J: Isolation of a novel tumor protein that induces resistance to natural killer cell lysis. J Immunol 1990;145:3516-3523. 46 Moretta A, Tambussi G, Bottino C, Tripodi G, Merli A, Cioccone E, Pantaleo G, Moretta L: A novel surface antigen expressed by a subset of human CD3- CDI6+ natural killer cells. Role in cell activation and regulation of cytolytic function. J Exp Med 1990;171:695-714. 47 Herberman RB, Reynolds CW, Ortaldo JR: Mechanism of cytotoxicity by natural killer cells. Annu Rev Immunol 1986;4:651-670. 48 Savary CA, Lotzova E: Phylogeny and ontogeny of NK cells; in Lotzova E, Herberman RB (eds): Immunology of Natural Killer Cells. Boca Raton, CRC Press, pp 46-52.
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MHC and NK Activity
JosOPe~a Rafael Solana ImmunologyUnit, Department of Biochemistry,Schoolof Medicine, Reina SofiaHospital, Universityof C6rdoba, Spain
9 . , * * Q . . ~ 1 7 6 1 7 6 1 7 6 1 7 6 ~ 1 7 6 1 7 6 1 7 6 1 7 6
Key Words Natural killer MHC class I antigen Cell lysis yIFN Transfection
Histocompatibility Antigens and Natural Killer Susceptibility I J e l o l o o o o o o o * o l o l o l t a o t . o l o o o o o l o . a t . o * ~ 1 7 6
J o o o * l * * J * o * o ~
Abstract The central question of the nature of the structure(s) involved in the recognition of targets by natural killer (NK) cells remains unresolved. Although NK-mediated cytotoxicity is not MHC-restricted, it has been suggested that these cells could recognize the targets more effectively in the absence of MHC class I antigens. In this paper we review the contradictory results obtained when studying the NK susceptibility of cell lines which constitutively express different levels of MHC antigens, or which have been induced to express MHC antigens by gene transfection or gamma-interferon treatment. Taken together, the results indicate that MHC antigens play a differential role in NK lysis depending on the nature of the target cells used; MHC class I antigens play a role in the NK resistance of cells from a hematopoietic lineage, but this does not extend to cells from other origins. The data reviewed also support the hypothesis that MHC class t antigens induced NK resistance by interfering with target structures, and that multiple NK molecules are involved in NK-mediated lysis as part of a possible advanced recognition system. * * 4 * o * ~
Introduction It is well known that natural killer (NK) cytotoxicity is involved in a wide series of defensive immunological functions. NK-mediated lysis implies previous recognition and binding of target and effector cells. Although different molecules have been reported to play a role in the interaction between these cells, their precise nature and function have not yet been clearly defined [ 1-4]. Contrary to
what occurs with the T lymphocytes which recognize antigens only when they are presented in association with major histocompatibility (MHC) antigens, NK-mediated lysis is not restricted by the histocompatibility products. Moreover, it has been suggested that MHC class I antigen expression on target cells reduces their susceptibility to be lysed. This hypothesis has stimulated a great deal of interest and controversy due to the conflicting results found by different authors in a
Prof. J. Pefia Department of Biochemistry School of Medicine Av. Men~ndez Pidal, s/n E-14004 C6rdoba (Spain)
9 1992 S. Karger AG, Basel 0257-277X/92/ 0112-013352.75/0
Table 1. Effect of increased MHC class I antigen expression on NK susceptibility of target cells from different origins
Model
Cell type
NK sensitivity
References
Murine Murine Murine Human Human Human Human Human
lymphoma (EL4, RBL5) lymphoma (YAC 1) fibrosarcoma (GR9 clones) tymphoblastoid (HBS, HMy2) EBV cell lines (721 mut.) EBV cell lines (MM-1 mut.) solid tumor cell lines solid tumor cell lines
block block block block block block no effect no effect
5, 19 7 8 10 i1 12 14 15-17
variety of experimental models. Thus, the susceptibility of tumor cells with different levels of MHC antigens to lysis by NK cells has been extensively studied. From a general point of view three particular experimental conditions have been used: (a)NK lysis of target cells expressing different levels of MHC antigens, (b) the effect of MHC gene transfection of target cells on NK susceptibility, and (c)the effect of gamma-interferon (yIFN) treatment on target MHC antigen expression and NK susceptibility. In this paper, the results obtained from these studies are reviewed and analyzed in order to evaluate the role that the MHC class I antigens on the target cells play in NK cell recognition and lysis.
NK Susceptibility of Cells Expressing Different Levels of MHC Antigens NK susceptibility of tumor cells with different levels of MHC class I antigens is heterogeneous (table 1). The initial observations, both in vivo and in vitro, demonstrating a relationship between decreased NK sensitivity and increased H-2 expression in variants of several murine lymphomas (YAC-1, RBL5, EL4) [5-7] gave rise to the hypothesis that one function of N K cells is to lyse cells that fail to express MHC antigens (missing-selfhypothe-
134
Pefia/Solana
sis). Thus, NK cells could be acting as a defensive system complementary to the recognition and elimination of target cells by Tc lymphocytes, where Tc cells would kill cells expressing self MHC class I antigens associated with altered or foreign peptides, and NK cells those with reduced MHC class I antigen expression. The missing-self hypothesis proposes that low levels of MHC antigens may confer susceptibility to NK lysis. A similar relationship between low expression of MHC class I antigens and NK susceptibility was obtained in clones from a murine fibrosarcoma [8], and B16 melanoma cells pretreated with yIFN and inoculated intravenously [9]. Using a panel of human cell lines derived from T lymphoblastoid cells and from a lymphoma B cell line (HMy2), Storkus et al. [10] found that NK susceptibility varied inversely with the level of target cell class I HLA antigen expression. This correlation has also been observed in other human EBV transformed B cell lines [ 11, 12]. However, these results cannot be extended to other types of tumors, as different studies show that HLA antigen expression has no effect on NK susceptibility when human cell lines derived from lung carcinomas [13], sarcoma or melanoma [ 14] are used. Our results (table 2) with cell lines derived from solid tumors also suggest that N K susceptibility is
MHC and NK Activity
Table 2. M H C expression and N K resistance of cell lines obtained from primary and metastatic brain tumors N K sensitivity + MHC + MHC -
4 6
6 5
Values represent the number of cases. Adapted from references 16 and 17.
independent of the level of HLA class I expression [ 15-17]. Cell lines expressing high levels of HLA antigens can be either NK resistant or NK susceptible, and those expressing nondetectable levels can also be resistant or susceptible to NK cytotoxicity. One possible explanation for the discrepancy in the results obtained by different investigators could be related to the nature of the different tumors used. Thus, when target cells from hematopoietic origin were analyzed, a significant effect of the MHC class I products on the susceptibility of the target cell to be lysed by NK cells was generally found. However, in studies with cell lines from solid tumors, no relationship between MHC class I expression and NK susceptibility was observed, indicating that target cell properties, other than the lack of MHC class I antigens, affect target cell sensitivity to NK lysis. In fact, NK cells interact with target cells through several surface molecules and their corresponding ligands [3, 18-20]. This can explain the contradictory results as these structures could be differentially expressed on tumor cells of different origin. This possibility has also been proposed by Ljunggrenn and Karre [ 19] who reinterpret the contradictory results in the literature within a multiple-
choice model. This model proposes that N K cells use different mechanisms for target recognition and lysis, and that one of these mechanisms is affected by MHC class I antigen expression. Two other nonexclusive interpretations can be given: (1) that MHC Ag expression and NK target structures are concurrently regulated in some but not all target cells (probably depending on the specific cell lineage or the factor(s) involved in malignant transformation), and (2)that MHC Ag are physically associated with NK target structures in certain target cells, blocking their recognition by the NK effectors (although depending on the cells, the target structures can be differentially expressed).
NK Susceptibility of Cells Transfected with MHC Class I Genes
The possibility of transfecting MHC genes into MHC-negative target cells has provided the opportunity to directly study whether or not MHC class I products affect NK susceptibility. Target susceptibility before and after transfection with MHC class I genes has been studied in both murine and human models. The results obtained (table 3), depend once again, on the target cells used. In murine models, transfection of H-2K b genes in hepatoma cells [21] and H-2Dp genes in lung carcinomas [22] has no direct effect on N K resistance. On the other hand, transfection of H-2 genes to an MHC-deficient murine lymphoma variant [23] and to a melanoma cell line [24] makes them resistant to NK lysis. When human target cells are considered, the results found by different authors demonstrate that whereas transfection of HLA class I or 13-2microglobulin genes induces resistance to NK lysis when EBV-transformed cell lines are used [25-28], HLA class I gene transfection does not significantly affect NK suscepti-
135
Table 3. Effect of MHC class I gene transfection on NK susceptibility of target ceils Model
Cell type
Transfecting genes
NK sensitivity
Reference
Murine Murine Murine Human Human Human Human Human Human
hepatoma (BW7756) lung carcinoma EL-4 mutant lung carcinoma (GLC2) lymphoma (DAUDI) lymphoblastoid (HMy2) lymphoblastoid (HMy2) lymphoblastoid (HMy2) cell lines (K 562, MOLT4)
H-2K b H-2DP
no effect no effect decreases no effect decreases decreases decreases decreases no effect
21 22 23 13 25 26 27 28 29
HLA class 1/132micro, 132 microglob, HLA class I ct1/ct2 domains HLA class I HLA class I
bility of target cells from other origins such as human lung carcinoma [13] or the classical NK targets, K562 or Molt4 [29]. Furthermore, it has been recently shown [30] that a single amino acid in the peptide binding groove of HLA can be responsible for the protective effect of NK lysis. In short, the results obtained from target cells transfected with MHC class I genes are not conclusive, the induction of resistance depending on the target cell used. The fact that transfection does not affect NK susceptibility when MHC gene products are transfected into cell lines of nonhematopoietic origin such as lung carcinoma [22] or hepatoma [21] in mouse, and human lung carcinoma [ 13], and that HLA class I antigens play a critical role in NK resistance in human cell lines transformed by EB virus [25-28] is of interest. It supports the view that MHC antigens play a differential role in NK recognition and lysis depending on the cells used as targets, and suggests that in some cell lines MHC class I antigens interact with the NK target structures blocking their recognition by effector cells. However, this model cannot be extended to all NK-susceptible target cells, corroborating the assumption that different mechanisms for target cell recognition and lysis are involved in NK cell activity.
136
Pefia/Solana
NK Susceptibility and MHC Levels in yIFN-Treated Cells IFN is being extensively used in therapy with contradictory results, and so its biological properties need to be further studied. It has been shown that 7IFN induces HLA molecule expression on a wide range of tumor cells [31], and it is generally agreed that treatment of NK-susceptible target cells with IFN results in a decreased susceptibility to lysis by NK cells [21, 24, 31-36]. The mechanism involved in NK resistance by 7IFN treatment are not fully understood [3, 17, 37-41], although it has been suggested that the changes in MHC antigen expression induced by this lymphokine could be responsible for NK blocking recognition and lysis [5, 23, 24] (table 4). In murine lymphomas or human K562 treated with 7IFN, a decreased N K susceptibility and increased HLA class I antigen expression were observed. However, IFN treatment can induce NK resistance without modifying MHC class I antigen expression in brain tumor cell lines [I 5, 17], sarcomas [14] and hepatomas [21]. Notwithstanding, the possible role of MHC antigens induced by 7IFN in resistance to NK lysis is difficult to evaluate. An example of these difficulties arises in two reports in which similar experi-
MHC and NK Activity
Table 4. NK susceptibility and MHC class I expression in 7IFNtreated target cells
Model
Cell type
MHC in- NK duction sensitivity
Reference
Murine Murine Murine
YAC- 1 BL-6 EL-4 EL-4 mutant lymphoma (RAJI) sarcoma ($4) melanoma (M 14) EBV transfected solid tumors K562 lung carcinoma (GLC2)
yes yes yes no no
decreases decreases decreases no effect decreases
7 24 23
no no yes yes
no effect decreases decreases decreases
12 17
Human
Human Human Human
mental approaches come to opposite conclusions: while K562 cells become NK resistant with yIFN treatment and not with HLA class I gene transfection [28, 42], murine EL4 variants become resistant to NK lysis with H-2 gene transfection but not with 7IFN treatment [23]. These data demonstrate once more that MHC expression cannot be used to explain 7IFN-mediated NK resistance in all cell lines. Moreover, in a more recent study we found that a non MHC-related structure, a tumor factor produced by the CAP-2 cell line (NK-RIF), also induces NK resistance without inducing MHC class I antigens [43-45]. In an attempt to further clarify how MHC antigens could participate in 7IFN-induced NK resistance, the different stages o f N K lysis have also been studied. NK lysis is the result of a multiple-step process in which the different stages involved in resistance need to be evaluated. Initially, NK effector ceils bind targets via an appropriate structure, forming conjugates [3, 4, 18, 36, 46-48]. After recognition, NK effector cells trigger or program lysis and release the cytolytic factor(s) (NKCF). Finally, NKCF irreversibly binds to the target cells leading to cell death.
14
13
In some of these studies, no relationship between conjugate formation and MHC antigen expression has been observed (e.g. in IFNtreated K562) [38, 42], indicating that the induction of NK resistance by MHC Ag is a post-binding event as represented in figure I. On the other hand, Storkus et al. [10] found such a correlation in a panel of human cell lines. In one of our studies on the NK lyric process using 7IFN-treated K562 and separated into HLA-positive an HLA-negative subsets, we observed that both populations formed a similar number of target-effector conjugates, although the HLA-positive population had a reduced capacity to trigger NK cell activation [42].
Conclusions
The results reviewed demonstrate that target MHC class I antigens play a clear role in NK resistance of murine lymphomas and melanomas and human EBV-transformed Bcell lines. Results also show that it is not possible to extend this function to cell lines of different origins, indicating that MHC antigens react differently to NK lysis depending on the
137
T a b l e 5. MHC expression and NK resistance in tumors of different nature
NK LYSIS
Cell line origin
TARGET
EFFECTOR )
MHC effect on NK lysis
Hematopoietic leukemias Solid tumors
block
no block
16 4
2 5
CELL
CELL
Values represent the number of reports using different experimental approaches.
O 9
i•loOoO0
NKCF
target ceils used (table 5). These findings support the hypothesis that multiple target structures are involved in NK-mediated lysis. In experimental models such as 7IFN-treated K562 ceils, the relationship between M H C antigens and N K resistance may be more a consequence o f a coordinate expression of both the N K target structure and the M H C products than o f a direct effect of the antigens. Furthermore, in those cases in which M H C is involved, the results suggest that they are probably interfering with target structures instead o f inducing an inhibitory signal for N K cells, as it is possible to render NK-sensi-
138
Pefia/Solana
Fig. 1. NK lysis is the result ofa multistep process, which starts with the recognition and binding of the target (first step). The effector adhesion molecules LFA-I (CD1 la/CD18) or CD2 bind to target structures ICAM-1 (CD54) or LFA-3 (CD58), respectively. Other NK-specific molecules are probably participating in the effector-target conjugate formation. This is followed by the NK effector triggering (second step) which involves hydrolysis of phosphatidyl-inositol, activation of protein kinase C, and Ca~-+mobilization. With the subsequent release of NKCF, and finally the binding of the NKCF to the target cell, cell death results (third step). MHC antigens could participate in some experimental models by interfering with the postbinding activation of the effector cells and blocking NK activation and the secretion of NKCF.
tive target cells resistant to N K lysis despite reduced M H C expression. Thus, further studies to determine the exact mechanisms o f N K lysis o f target ceils from different origins are necessary, especially as it has recently been suggested [46] that N K cells possess an advanced recognition system.
Acknowledgements The authors thank Ms. Christine Mendez and Ms. M.L. Velarde for their collaboration in the preparation of the manuscript. This work was supported by grants from the CICYT and FIS (Spain).
MHC and NK Activity
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References 1 Chambers WH, Vujanovic LN, De Leo AB, Olszowy MW, Herberman RB, Hiserodt JC: Monoclonal antibody to a triggering structure expressed on rat natural killer cells and adherent lymphokine- activated killer cells. J Exp Med 1989;169: 1373-1383. 2 Harris DT, Jaso-Friedmann L, Devlin RB, Koren HS, Evans SL: Identification of a human natural killer cell target cell antigen with monoclonal antibodies. J Immunol 1989; 143:727-735. 3 Trinchieri G: Biology of natural killer cells. Adv Immunol 1989;47: 187-342. 4 Ortaldo JR, Hiserodt JC: Mechanisms of target cell killing by natural killer cells. Curr Opin lmmunol 1990: 2: 39-44. 5 Karre K, Ljunggren JH: Piontek G, Kiessling F: Selective rejection of H2 deficient lymphoma variants suggests alternative immune defense strategy. Nature 1986;319:675-678. 6 Karre K: Role of target histocompatibility antigens in regulation of natural killer activity: A reevaluation and a hypothesis, in Herberman RB, Callewaert D (eds): Mechanisms of Cytotoxicity by Natural Killer cells. Orlando, Academic Press, 1985, pp 81-85. 7 Piontek GE, Taniguchi K, Ljunggren H, Gronberg A, Kiessling R, Klein G, Karre K: YAC-I MHC class I variants reveal an association between decreased NK sensitivity and increased H-2 expression after interferon treatment or in vivo passage. J Immunol 1985;135:42814288. 8 Algarra I, Ohlen C, Perez M, Ljiinggren HG, Klein G, Garrido F, Karre K: MHC class I deficient cells within a heterogeneous fibrosarcoma show elevated NK sensitivity and reduced survival in the lungs after intravenous administration. Int J Cancer 1989;44:675-680.
9 Taniguchi K, Petersson M, Hoglund P, Kiessling R, Klein G, Karre K: Interferon 7 induces lung colonization by intravenously inoculated B 16 melanoma ceils in parallel with enhanced expression of class I mayor histocompatibility complex antigens. Proc Natl Acad Sci (USA) 1987;84: 3405-3409. 10 Storkus WJ, Howell DN, Salter RD, Dawson JR, Cresswell P: NK susceptibility varies inversely with target cell class I HLA expression. J Immuno11987;138:1657-1659. l I Harel-Bellan A, Quillet A, Marchiol C, Demars R, Tursz T, Fradelizi D: Natural killer susceptibility of human cells may be regulated by genes in the HLA region of chromosome 6. Proc Natl Acad Sci (USA) 1986;8: 5688-5692. 12 Ohl~n C, Bejarano MT, Grrnberg A, Torsteinsdottir, S, Fransksson L, Ljunggren HG, Klein E, Klein G, K/irre K: Studies ofsublines selected for loss of HLA expression from an EBV-transformed lymphoblastoid cell line: Changes in sensitivity to cytotoxie T cells activated by allostimulation and natural killer cells activated by IFN or IL-2. J lmmunol 1989;142:3336-3341. 13 Stam N J, Kast WM, Voordouw AC, Pastoors LB, Van der Hoeven FA, Melief CJM, Ploegh IlL: Lack of correlation between levels of MHC class I antigen and susceptibility to lysis of small cellular lung carcinoma by natural killer cells. J Immuno11989;142:4113-4117. 14 de Fries R, Golub SH: Interferon reduces the sensitivity of cultured and fresh human tumor cells to lysis by lymphokine-activated killer cells. Nat Immun Cell Growth Regul 1988;7:65-76. 15 Alonso C, Serrano R, Solana R, Pefia J: Natural killer susceptibility of brain tumor cell lines inversely correlates with the degree of cell differentiation. Int Arch Allergy Appl Immunol 1989;89:169-172. 16 Pefia J, Solana R, Alonso C, Santamar/a M, Serrano R, Ramirez R, Carracedo J: MHC class I expression on human tumor cells and their susceptibility to NK lysis. J Immunogenet 1989; 16:407-412.
17 Pefia J, Alonso C, Solana R, Serrano R, Carracedo J, Ramirez R: Natural killer susceptibility is independent of HLA class I antigen expression on cell lines obtained from human solid tumors. Eur J Immunol 1990;20: 2445-2449. 18 Lotzova E, Ades EW: Natural immune killer cells definition, heterogeneity, lytic mechanism, genetics and clinical application. Highlights of the fifth international workshop on NK cells. Nat Immun Cell Growth Regul 1989;8:1-7. 19 Ljunggren HG, Karre K: In search of the 'missing self: MHC molecules and NK cells recognition. Immunol Today 1990;11:237-244. 20 Solana R, Serrano R, Pefia J: MHC antigens in NK recognition and lysis. lmmunol Today 1991 ;12:95. 21 Nishimura M, Stroynowski I, Hodd L, Ostrand-Rosenberg S: H-2K b antigen expression has no effect on natural killer susceptibility and tumorigenicity o f a murine hepatoma. J Immunol 1988;141:4403-4409. 22 Dennert G, Landou C, Lord EM, Bahler DW, Frelinger JK: Lysis of a lung carcinoma by poly I-C-induced natural killer cells is independent of the expression of class I histocompatibility antigens. J lmmunol 1988: 140:2472-2475. 23 Sturmhofel K, Hammerling G: Reconstitution of H-2 class I expression by gene transfection decreases susceptibility to natural killer cells of an EL4 class I loss variant. Eur J Immunol 1990;20:171-175. 24 Gorelik E, Gunji Y, Herberman R: H-2 antigen expression and sensitivity of BL6 melanoma cells to natural killer cell cytotoxicity. J Immunol 1988; 140:2096-2101. 25 Quillet A, Presse F, Marchiol-Fournigault C, Harel-Bellan A, Benbunan M, Ploegh H, Fradelizi D: Increased resistance to non-MHC-restricted cytotoxicity related to HLA A, B expression. Direct demonstration using ~2-microglobulin transfected Daudi cells. J Immunol 1988; 141:17-20.
139
26 Storkus W J, Alexander J, Payne JA, CressweU P, Dawson JR: The ctl Rt2 domains of class I HLA molecules confer resistance to natural killing. J Immuno11989;143:3853-3857. 27 Storkus WJ, Alexander J, Payne AJ, Dawson JR, Cresswell P: Reversal of natural kilIing susceptibility in target ceils expressing transfected HLA class I genes. Proc Natl Acad Sci (USA) 1989;86:2361-2364. 28 Sbimizu Y, Demurs R: Demonstration by class I gene transfer that reduced susceptibility of human cells to natural killer cell-mediated lysis is inversely correlated with HLA class I antigen expression. Eur J Immuno11989;19:447-451. 29 Leiden JM, Kornbluth J: Susceptibility to natural killer cell mediated cytolysis is independent of the level of target cell class I HLA expression; in Ades EW, Lopez C (eds): Natural Killer Cells and Host Defense. 5th Int NK Cells Workshop. Basel, Karger, pp 198-206. 30 Storkus WJ, Salter RD, Alexander J, Ward FE, Ruiz RE, Creswell P, Dawson JR: Class I induced resistance to natural killing: Identification of nonpermissive residues in HLA-A2. Proc Natl Acad Sci (USA) 1991 ;88:5989-5992. 31 Woodroofe MN, Hayes GM, Cuzner L: Fc receptor density, MHC antigen expression and superoxide production are increased in interferon gamma treated microglia isolated from adult rat brain. Immunology 1989;68:421-425. 32 Giuliani-Bonmassar A, Graziani L, Frati L, Bonmassar E: Interferoninduced changes in the susceptibility of murine and human lymphoma cells to natural cytotoxic lymphocytes, lnt J Tissue React 1984;6:3542. 33 Moore W, White M, Potter MR: Modulation of target cell susceptibility to human natural killer cells by interferon. Int J Cancer 1980;25: 565-570.
34 Trinchieri G, Santoli D: Antiviral activity induced by culturing lymphocytes with tumor-derived or vires-transformed cells. Enhancement of human natural killer cell activity by interferon and antagonistic inhibition of susceptiblity of target ceils to lysis. J Exp Med 1978;147:13t41321. 35 Welsh RM, Karre K, Hansson M, Kunker LA, Kiessling RW: Interferon-mediated protection of normal and tumor target cells against lysis by mouse natural killer cells. J Immunol 1981;126:219-224. 36 Witte T, Wordelmann K, Schmidt RE: Heterogeneity of human natural killer cells in the spleen. Immunology 1990;69:166-172. 37 Gronberg A, Kiessling R, Masucci G, Guevara LA, Eriksson E, Klein G: Gamma-IFN (IFN-'/) produced during effector and target interactions renders target ceils less susceptible to NK-cell-mediated lysis, lnt J Cancer 1983;32:609-615. 38 Gronberg A, Ferm MT, Reynolds CW, Ortaldo JR: IFN-gamma treatment of K562 cells inhibits natural killer cell triggering and decreases the susceptibility to lysis by cytoplasmic granules from large granular lymphocytes. J Immunol 1988;14: 4397-4402. 39 Powell J, Stone J, Chan VC, Yang Z, Leatherbury A, Sell KW, WiktorJedrzejczak W, Ahmed-Ansari A: Interferon-gamma-treated K562 target cells distinguish functional NK cells from lymphokine-activated killer (LAK) cells. Cell Immuno11989;118:250-259. 40 Uchida A, Vanky F, Klein E: Natural cytotoxicity of human blood lymphocytes and monocytes and their cytotoxic factors: Effect of interferon in target cell susceptibility. J Natl Cancer Inst 1985;75:849854.
41 Wright SC, Bonavida B: Studies on the mechanism of natural killer cellmediated cytotoxicity. IV. Interferon induced inhibition of NK target cell susceptibility to lysis is due to a defect in their ability to stimulate release of natural killer cytotoxic factors (NKCF). J lmmunol 1983; 130:2965-2972. 42 Ramirez R, Solana R, Carracedo J, Alonso MC, Pefia J: Mechanisms involved in NK resistance induced by interferon-'/. Cell Immunol 1992; 140:248-256. 43 Serrano R, Alonso C, Solana R, Monserrat J, Mufioz J, Pefia J: Identification of a tumor factor inducing resistance to NK cell lysis. Immunol Lett 1989;20:311-316. 44 Solana R, Alonso C, Ramirez R, Carracedo J, Serrano R, Yiangou Y, Pefia J: Analysis of the mechanisms involved in NK resistance induced by a new tumor factor NK-RIF. Cell lmmunol 1990;130:244-251. 45 Serrano R, Yiangou Y, Solana R, Sachs JA, Pefia J: Isolation of a novel tumor protein that induces resistance to natural killer cell lysis. J Immunol 1990;145:3516-3523. 46 Moretta A, Tambussi G, Bottino C, Tripodi G, Merli A, Cioccone E, Pantaleo G, Moretta L: A novel surface antigen expressed by a subset of human CD3- CDI6+ natural killer cells. Role in cell activation and regulation of cytolytic function. J Exp Med 1990;171:695-714. 47 Herberman RB, Reynolds CW, Ortaldo JR: Mechanism of cytotoxicity by natural killer cells. Annu Rev Immunol 1986;4:651-670. 48 Savary CA, Lotzova E: Phylogeny and ontogeny of NK cells; in Lotzova E, Herberman RB (eds): Immunology of Natural Killer Cells. Boca Raton, CRC Press, pp 46-52.
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MHC and NK Activity
