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IN IMMUNOLOGY

IL6 and AIDS 0. Martinez-Maza Departments

of Obstetrics & Gynecology and Microbiology & Immunology, UCLA School of Medicine, Los Angeles, CA (USA)

Introduction

AIDS is a transmissible form of immune deficiency caused by HIV infection, that is characterized by a decrease in CD4 T-cell number and function, along with numerous other immune defects (Rosenberg and Fauci, 1990; Lane and Fauci, 1985). Paradoxically, a marked increase in immune activation accompanies this profound T-cell deficiency; elevated levels of markers for immune activation, as well as elevated serum immunoglobulin (Ig), increased spontaneous Ig secretion and elevated levels of circulating activated B cells, are seen in AIDS and related conditions (Lane et al., 1983; Martinez-Maza et al., 1987 ; Edelman and Zolla-Pasner, 1989 ; Fahey et al., 1990). Elevated levels of various cytokines, including IL6, are also seen in HIV infection (Rosenberg and Fauci, 1990; Merrill and Chen, 1991). In fact, the interaction of human cells with HIV can result in the increased production of cytokines (Merrill and Chen, 1991). This HIV infection-associated overproduction of cytokines has the potential to contribute to AIDS pathogenesis by upregulating HIV replication, by contributing to the development and growth of AIDS-associated cancers, or by inducing immune dysfunction. IL6 levels in vivo in HIV

infection

Since immune dysfunction is a central observation in AIDS, it is not surprising that various changes in cytokine levels have been reported in this syndrome. Elevated levels of serum cytokines, cytokine production and soluble cytokine receptors have been seen in AIDS and in HIV infection. Elevated levels of serum/plasma IL6 were detected in the majority of HIV-infected donors by most groups that have examined this issue (Breen et al., 1990 ; Birx et al., 1990; Honda et al., 1990; Lafeuillade et al., 1991; Rautonen et al., 1991; de Wit et al., 1991). Also, increased levels of spontaneous IL6 production, as well as increased levels of in vivo IL6 mRNA expression, were seen in peripheral blood mononuclear cells (PBMC) isolated from HIV-infected donors (Breen

et al., 1990; Birx et al., 1990). However, one study reported no detectable increase in serum IL6 or IL6 production in HIV-infected donors (Amadori et al., 1991). It is important to note that most commercially available IL6 ELISA do not reliably detect serum IL6, and that human sera must be treated prior to testing in IL6 bioassays (Breen et al., 1990). Therefore, technical difficulties could account for some of the reported differences in serum IL6 in AIDS. Monocytes appear to be responsible for the major portion of the IL6 produced by PBMC isolated from HIV-infected donors (Breen et al., 1990; Birx et al., 1990). In recent preliminary studies, we detected increased numbers of IL6-containing cells in PBMC from HIV-infected donors, using a flow cytometric technique based on the permeabilization of the cell membrane to allow staining with anti-IL6 serum while maintaining cellular integrity (Sander et al., 1991). Using this technique, monocytes showed the greatest HIV infection-associated increase in IL6-containing cells (unpublished observation). While most reports indicate that IL6 levels are elevated in HIV infection, there is no general agreement as to whether there is an association between disease stage and serum or plasma IL6 level in HIV infection. Birx and co-workers (1990) found elevated serum IL6 in HIV-infected people in Walter Reed stages l-4, with much lower serum IL6 levels in more advanced disease (Walter Reed stages 5/6). Others have reported that symptomatic HIV-infected donors had increasing serum/plasma IL6 levels (Honda et al., 1990), or, alternatively, that there was no apparent association between IL6 level and severity of HIV-associated disease (Breen et al., 1990). Additional studies are needed to define the association between in vivo IL6 levels and the presence or extent of HIV-associated clinical disease. Positive correlations have been noted between serum IL6 levels and serum-soluble IL2 receptor (sIL2R) levels (Honda et al., 1990). Also, increased in vivo levels of an acute phase reactant known to be induced by IL6 (C-reactive protein, CRP) were seen to accompany the increase in IL6 seen in HIV infection (Breen et al., 1990). Also, increased serum

INTERLEUKIN levels of soluble IL6 receptor (sIL6R) were detected in HIV-infected donors (Honda et al., 1992). The effect of antiretroviral treatment on in vivo IL6 levels is a question that is of particular interest, since HIV-infected patients undergoing long-term antiretroviral treatment with zidovudine (AZT) have a high incidence of B-cell lymphoma (Pluda et al., 1990; Beral et al., 1991). Since IL6 is a B-cellstimulating factor, and since IL6 has been seen to act as an autocrine/paracrine growth factor for human myeloma cells (Hirano et al., 1990), we considered the possibility that a zidovudine-treatment-associated increase in IL6 levels could contribute to the pathogenesis of AIDS-associated B-cell lymphoma. Our preliminary results indicate that this does not appear to be the case; serum IL6 levels in HIV-infected donors decreased following the initiation of treatment with zidovudine (unpublished observation). Induction

of IL6 production

by HIV

While the mechanisms that result in increased cytokine production in HIV infection have not been fully defined, it is clear that HIV can interact with human cells, leading to the induction of IL6 production. Exposure of various human cells to HIV preparations or HIV-encoded products has been seen to result in cytokine (IL6, ILl, TNF-a) production (Merrill and Chen, 1991). For instance, exposure of PBMC from healthy, HIV-seronegative donors to HIV (infectious or inactivated virus) was seen to lead to IL6 production (Nakajima et al., 1989). The bulk of HIV-induced IL6 was produced by monocyte/macrophages. Our recent preliminary studies indicated that the THP-1 human monocyte cell line could be induced to produce IL6 by HIV, or by HIV envelope protein (unpublished observations). Also, AIDS-associated Kaposi’s sarcoma cells could be induced to produce increased levels of IL6 on exposure to recombinant HIV tat protein, or following transfection with the HIV tat gene (Martinez-Maza et al., in press). Some workers have suggested that HIV does not induce IL6 production, contending that contaminating endotoxin in the HIV preparations used in other studies induced monokine production (Molina et al., 1990). However, this appears unlikely, since a specific anti-HIV serum blocked HIV-induced IL6 production (Nakajima et al., 1989), and since our recent work indicates that HIV preparations induced > 20 times more IL6 production than would be predicted based on the endotoxin content of these virus preparations (unpublished observations). Also, various recent reports indicate that HIV-encoded products can induce IL6 production. HIV gp120 envelope protein was seen to stimulate monokine production, including the production of IL6 (Clouse

6

165

et al., 1991). Also, Oyaizu and co-workers showed that HIV envelope glycoproteins gp120 and gp160 (endotoxin-free) could induce IL6 production by T cells and monocytes (Oyaizu et al., 1991). Therefore, it appears that HIV-encoded products, particularly HIV envelope protein, can interact with human cells, leading to IL6 gene expression. The cellular receptor(s) for HIV that leads to signal transduction and to monokine gene expression has not been defined, although it appears that CD4 could be involved (Merrill et al., 1989). While most HIV gp120 binding to T cells occurs via the CD4 molecule, most binding of gp120 to monocytes does not appear to occur via CD4 (Finbloom et al., 1991). Our studies support this observation : using a flow cytometric system to measure binding of inactivated HIV to human cells, we saw that anti-CD4 monoclonal antibody blocked nearly all HIV binding to T-cell lines, but only a fraction of HIV binding to monocytes, suggesting that monocytes can bind HIV via a non-CD4 receptor (unpublished observation). IL6 and AIDS-associated

B-cell hyperstimulation

Hypergammaglobulinaemia and chronic B-cell stimulation are seen typically in AIDS (Lane et al., 1983 ; Martinez-Maza et al., 1987). Since IL6 is a potent B-cell stimulatory factor, the overproduction of this cytokine in HIV infection could contribute to this B-cell hyperstimulation (Breen et al., 1990; Amadori et al., 1991). Elevated levels of IL6 significantly correlated with elevated serum IgG levels in HIVinfected donors (Birx et al., 1990). Also, elevated serum IL6 levels were associated with elevated serum IgG and IgA in children with HIV infection (Rautonen et al., 1991). Spontaneous in vitro Ig production by PBMC from HIV-infected donors was inhibited by the addition of anti-IL6 serum or by depletion of accessory cells ; addition of IL6 to accessory celldepleted cultures counteracted the decrease in spontaneous Ig production (Amadori et al., 1991). Together, these results suggest that IL6 overproduction in HIV infection could contribute to B-cell hyperstimulation and to hypergammaglobulinaemia. IL6 and AIDS-associated

cancers

Various cytokines, including IL6, and oncostatin M (OSM), which is a member of an IL6-like family of cytokines (Rose and Bruce, 1991), can act as autocrine/paracrine growth factors for AIDSassociated Kaposi’s sarcoma (KS) cells (Miles et al., 1990, 1992; Ensoli et al., 1989; Corbeil et al., 1991). Also, serum IL6 levels were seen to be higher in patients with AIDS-KS than in asymptomatic HIVinfected donors (De Wit et al., 1991). In recent studies, we saw that several cytokines, including IL1

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and TNF-a, could induce KS cell growth in vitro, and that this increased growth was accompanied by an increase in IL6 production (Martinez-Maza et al., 1992; and unpublished observations). Inhibition of endogenous IL6 production, using an IL6 antisense oligonucleotide (Miles et al., 1990), resulted in the inhibition of most KS cell proliferation induced by IL1 or TNF-a, suggesting that the KS cell proliferation induced by these cytokines was mediated in part by the induction of IL6 production by KS cells (Martinez-Maza et al., in press). However, OSMinduced KS cell growth was not as significantly affected by this treatment, suggesting that OSM has a more direct growth-enhancing effect on KS cells (Miles et al., 1992). Interestingly, IL6 and OSM share part of their receptor structure: the specific cellular receptors for

these cytokines both utilize the larger subunit (gpl30) of the IL6 receptor (Gearing et al., 1992; Palca, 1992). While the IL6 receptor is composed of this gp130 molecule in association with a smaller (80 kDa) subunit (Hirano et al., 1990), the OSM receptor is made up of the IL6 receptor gpl30 molecule in association with the LIF (leukemia-inhibitory factor) receptor. Therefore, the overlapping biological activities of IL6 and OSM on KS cells can be explained, in part, by the sharing of receptor molecules. We have concluded that IL6 and OSM contribute to the pathogenesis of AIDS-KS, and that KS cell growth induced by various cytokines may be mediated partly by the induction of KS-cell-produced IL6. IL6 also could contribute to the development of AIDS-related B-cell lymphoma, both by acting as a chronic stimulus to B cells in HIV-infected people,

B CELL LYMPHOMA ?

c-myc/lg

gene

translocation

f J0 -0

4 t

hyper-lg other

HIV :

production

IL-6 cytokines

/ 0Cl Q

PROLIFERATION OF KS CELLS

HIV-INFECTED CELL

INCREASED

t

HIV PRODUCTION

Fig. 1. Central role of IL6 in AIDS pathogenesis. IL6 production, as well as the production of other cytokines, can be induced by contact between human monocytes (and other cell types) and HIV or HIV-encoded products. This increased IL6 production could then contribute to AIDS pathology in various ways,including the induction of B-cell hyperstimulation and hypergammaglobulinaemia, the enhancement of Kaposi’s sarcoma (KS) cell growth, and the induction of HIV replication. IL6 and other cytokines can also act as autocrine growth factors for KS cells.

INTERLEUKIN

leading to an increase in the number of B cells susceptible to a genetic accident (c-myc/Ig gene translocation) that would lead to lymphoma, or more directly, by acting as an autocrine or paracrine growth factor for AIDS lymphoma cells. At this time, we are examining the role of IL6 in AIDS lymphomagenesis.

4

these cytokines can enhance HIV production (fig. 1) (Merrill and Chen, 1991; Rosenberg and Fauci, 1990). Therefore, the HIV-induced production of IL6 could contribute directly to the extension of HIV infection and could thereby play a central role in the pathogenesis of AIDS. Acknowledgements

Induction

of HIV replication

by IL6

IL6 overproduction could contribute to the pathogenesis of AIDS and related conditions in other ways. Perhaps the most direct role for IL6 in the pathogenesis of AIDS involves the ability of this cytokine to act as a potentiator of HIV replication. Several cytokines can enhance HIV replication (Rosenberg and Fauci, 1990). Initial studies showed that a monokine-enriched supernatant could greatly enhance virus production by HIV-infected T cells (Clouse et al., 1989). Subsequently, TNF-a was seen to be a potent inducer of HIV replication in infected T cells and monocytes (Clause et al., 1989; Poli et al., 1990; Okamoto et al., 1989). IL6 (and ILl) also were seen to upregulate the production of HIV in infected monocytes (Poli ef al., 1990; TsunetsuguYokota and Honda, 1990; Rieckmann et al., 1991; von Briesen et al., 1991). IL6 synergizes with TNF-a in the induction of latent HIV expression (Poli ef al., 1990). Rieckmann and coworkers (1991) found that culture supernatants from B cells isolated from HIVinfected donors could induce HIV expression, while supernatants of B cells from HIV-negative donors did not. B cells isolated from HIV-infected donors were seen to produce greatly increased levels of IL6 and TNF-a; antibodies to these cytokines abolished the capacity to induce HIV replication, indicating that the spontaneous production of these cytokines by B cells from HIV-infected donors resulted in the enhancement of HIV replication (Rieckmann et al., 1991). While TNF-a and IL1 appear to enhance HIV replication by acting at the level of transcription, IL6 enhances HIV expression at multiple levels (Israel et al., 1989; Osborn et al., 1989; Poli et al., 1990). IL6-enhanced HIV replication does not appear to act at the transcriptional level and does not result in the accumulation of HIV RNA; however, when IL6 and TNF-u synergistically enhance HIV replication, increased HIV RNA levels are seen (Poli et al., 1990). Therefore, IL6 appears to enhance HIV expression by post-transcriptional mechanisms when acting alone, and by increasing transcription when acting in synergy with TNF-cl. HIV-induced cytokines, including IL6, could act in a positive autocrine loop, resulting in the amplification of HIV replication, since cytokine (ILl, TNFu, IL6) production can be induced by HIV, and since

I would like to thank Drs. E.C. Breen, T. Hirano, T. Kishimoto, S.A. Miles, K. Nakajima, Ms. M. Vander Meyden and Mr. A.R. Rezai and D. Widnoy for their collaboration and their many contributions to the studies discussed here. This work was supported in part by grants from the NIH (CA01588. CA57152, A172631, AI24691), and by the California Universitywide AIDS Research Program (R9lLA149).

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Beral, V., Peterman, T., Berkelman, R. & Jaffe, H. (1991), AIDS-associatednon-Hodgkin lymphoma. Lancer, 337, 805-809. Birx, D.L., Redfield,R.R., Tencer,K., Fowler, A., Burke, D.S. & Tosato, Cl. (1990),Induction of interleukin 6 during human immunodeficiency virus infection. Blood, 76, 2303-2310. Breen,E.C., Rezai,A.R., Nakajima, K., Beall, G.N., Mitsuyasu,R.T., Hirano, T., Kishimoto, T. &MartinezMaza, 0. (1990), Infection with HIV is associated with elevated IL-6 levels and production. J. Immunol., 144, 480-484. Clouse,K.A., Powell, D., Washington, I., Poli, G., Strebel, K., Farrar, W., Barstad, P., Kovacs, J., Fauci, A.S. & Folks, T.M. (1989), Monokine regulation of human immunodeficiency virus-l expressionin a chronicallyinfectedhumanT cell clone.J. Immunol., 142, 431-438. Clouse,K.A., Cosentino,L.M., Weih, K.A., Pyle, S.W., Robbins, P.B., Hochstein, H.D., Natarajan, V. & Farrar, W.L. (1991),The HIV-l gp120envelopeprotein hasthe intrinsic capacity to stimulatemonokine secretion. J. Immunol., 147, 2892-2901. Corbeil, J., Evans, L.A., Vasak, E., Cooper, D.A. & Penny, R. (1991),Culture and propertiesof cellsderived from Kaposi’ssarcoma.J. Immunol., 146,2912-2916. De Wit, R., Raasveld, M.H., ten Berge, R.J., van der

Wouw,P.A.,

Bakker, P.J.&Veenhof,C.H.

(1991),

Interleukin-6 concentrationsin the serumof patients with AIDS-associatedKaposi’ssarcomaduring treatment with interferon-alpha. J. int. Med., 229, 539-542. Edelman, A.S. & Zolla-Pasner, S. (1989), AIDS: a syndrome of immune dysregulation, dysfunction, and deficiency. FASEB J., 3, 22-29. Ensoli, B., Nakamura,S., Salahuddin,S.Z., Biberfeld, P., Larsson, L., Beaver, B., Wong-Staal, F. & Gallo,

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R.C. (1989), AIDS-Kaposi’s sarcoma-derived cells express cytokines with autocrine and paracrine growth effects. Science, 243, 223-226. Fahey, J.L., Taylor, J.M.G., Detels, R., Hofmann, B., Melmed, R., Nishanian, P. & Giorgi, J.V. (1990), The prognostic value of cellular and serologic markers in infection with human immunodeficiency virus type 1. New Engl. J. Med., 322, 166-172. Finbloom, D.S., Hoover, D.L. & Meltzer, MS. (1991), Binding of recombinant HIV coat protein gp120 to human monocytes. J. Immunol., 146, 1316-1321. Gearing, D.P., Comeau, M.R., Friend, D.J., Gimple, S.D., Thut, C. J., McGourty, J., Brasher, K.K., King, J.A., Gillis, S., Mosley, B., Ziegler, S.F. & Cosman, D. (1992), The IL-6 signal transducer, gp130, an oncostatin M receptor and affinity converter for the LIF receptor. Science, 255, 1434-1437. Hirano, T., Akira, S., Taga, T. & Kishimoto, T. (1990), Biological and clinical aspects of interleukin 6. 1mmunol. Today, 11, 443-449. Honda, M., Kitamura, K., Mizutani, Y., Oishi, M., Arai, M., Okura, T., Igarahi, K., Yasukawa, K., Hirano, T. & Kishimoto, T. (1990), Quantitative analysis of serum IL-6 and its correlation with increased levels of serum IL-2R in HIV-induced diseases. J. Immunol., 145, 4059-4064. Honda, M., Yamamoto, S., Cheng, M., Yasukawa, K., Suzuki, H., Saito, T., Osugi, Y., Tokunaga, T. & Kishimoto, T. (1992), Human soluble IL-6 receptor: its detection and enhanced release by HIV infection. J. Immunol., 148, 2175-2180. Israel, N., Hazan, U., Alcami, J., Munier, A., ArenzanaSeisdedos, F., Bachelerie, F., Israel, A. & Virelizier, J.-L. (1989), Tumor necrosis factor stimulates transcription of HIV-l in human T lymphocytes, independently and synergistically with mitogens. J. Immunol., 143, 3956-3960. Lafeuillade, I., Poizot-Martin, R., Quilichini, R., Gastaut, J .A., Kaplanski, S., Farnarier, C., Mege, J.L. & Bongrand, P. (1991), Increased interleukin-6 production is associated with disease progression in HIV infection. AIDS, 5, 1139-1140. Lane, H.C. & Fauci, A.S. (1985), Immunologic abnormalities in the acquired immune deficiency syndrome. Ann. Rev. Immunol., 3, 477-500. Lane, H.C., Masur, H., Edgar, L.C., Whalen, G., Rook, A.H. & Fauci, A. (1983), Abnormalities of B-cell activation and immunoregulation in patients with the acquired immunodeficiency syndrome. New Engl. J. Med., 309, 453-458. Martinez-Maza, O., Crabb, E., Mitsuyasu, R.T., Fahey, J.L. & Giorgi, J.V. (1987), Infection with the human immunodeficiency virus (HIV) is associated with an in vivo increase in B-lymphocyte activation and immaturity. J. Immunol., 138, 3720-3725. Martinez-Maza, O., Rezai, A.R., Magpantay, L., Klashman, D.J., Johnson, M.T., Watson, J.M., Hirano, T., Kishimoto, T. &Miles, S.A. (1992), Interleukin-6: role in AIDS-associated Kaposi’s sarcoma, in “IL-6: physiopathology and clinical potentials” (M. Revel). Raven Press, New York (in press). Merrill, J.E. & Chen, I.S. (1991), HIV-l, macrophages, glial cells, and cytokines in AIDS nervous system disease. FASEB J., 5, 2391-2397. Merrill, J.E., Koyanagi, Y. & Chen, I.S. (1989),

Interleukin-1 and tumor necrosis factor alpha can be induced from mononuclear phagocytes by human immunodeficiency virus type 1 binding to the CD4 receptor. J. Virol., 63, 4404-4408. Miles, S.A., Rezai, A.R., Salazar-Gonzalez, J .F., Van der Meyden, M., Stevens, R.H., Logan, D.M., Mitsuyasu, R.T., Taga, T., Hirano, T., Kishimoto, T. & Martinez-Maza, 0. (1990), AIDS Kaposi’s sarcomaderived cells produce and respond to interleukin-6. Proc. nat. Acad. Sci. (Wash.), 87, 4068-4072. Miles, S.A., Martinez-Maza, O., Rezai, A., Magpantay, L., Kishimoto, T., Nakamura, S., Radka, S.F. Rr Linsley, P. (1992), Oncostatin-M is a potent mitogen for AIDS-Kaposi-sarcoma-derived cells. Science, 255, 1432-1434. Molina, J.-M., Scadden, D.T., Amirault, C., Woon, A., Vannier, E., Dinarello, C.A. & Groopman, J.E. (1990), Human immunodeficiency virus does not induce interleukin-1, interleukin-6, or tumor necrosis factor in mononuclear cells. J. Virol., 64, 2901-2906. Nakajima, K., Martinez-Maza, O., Hirano, T., Breen, E.C.. Nishanian, P.G., Salazar-Gonzalez, J., Fahey, J.L. 8c Kishimoto, T. (1989), Induction of interleukin-6 (BSF2/IFN-br) production by HIV. J. Immunol., 142, 531-536. Okamoto, T., Matsuyama, T., Mori, S., Hamamoto, Y., Kobayashi, N., Yamamoto, N., Josephs, SF., WongStaal, F. & Shimotohno, K. (1989), Augmentation of human immunodeficiency virus type 1 gene expression by tumor necrosis factor alpha. AIDS Res. Hum. Retroviruses, 5, 131-138. Osborn, L., Kunkel, S. & Nabel, G.J. (1989), Tumor necrosis factor-a and interleukin-1 stimulate the human immunodeficiency virus enhancer by activation of the nuclear factor kB. Proc. nat. Acad. Sci. (Wash.), 86, 2336-2340. Oyaizu, N., Chirmule, N., Ohnishi, Y., Kalyanaraman, V.S. & Pahwa, S. (1991), Human immunodeficiency virus type 1 envelope glycoproteins gp 120 and gp 160 induce interleukin-6 production in CD4+ T-cell clones. J. Virol., 65, 6277-6282. Palca, J. (1992). Kaposi’s sarcoma gives on key fronts. Science, 255, 1352. Pluda, J.M., Yarchoan, R., Jaffe, E.S., Feuerstein, I.M., Solomon, D., Steinberg, S.M., Wyvill, K.M., Raubitschek, A., Katz, D. & Broder, S. (1990), Development of non-Hodgkin lymphoma in a cohort of patients with severe human immunodeficiency virus (HIV) infection on long-term antiretroviral therapy. Ann. int. Med., 113, 216-282. Poli, G., Bressler, P., Kinter, A., Duh, E., Timmer, W.C., Rabson, A., Justement, J.S., Stanley, S. & Fauci, A.S. (1990), Interleukin-6 induces human immunodeficiency virus expression in infected monocytic cells alone and in synergy with tumor necrosis factor alpha by transcriptional and post-transcriptional mechanisms. J. exp. Med., 172, 151-158. Rautonen, J., Rautonen, N., Martin, N.L., Philip, R. & Wara, D.W. (1991), Serum IL-6 concentrations are elevated and associated with elevated tumor necrosis factor-alpha and immunoglobulin G and A concentrations in children with HIV infection. AIDS, 5, 1319-1325. Rieckmann, P., Poli, G., Kehrl, J.H. & Fauci, A.S. (1991), Activated B lymphocytes from human immunodefi-

INTERLEUKIN ciency virus-infected individuals induce virus expression in infected T cells and a promonocytic cell line, UI. J. exp. Med., 173, l-5. Rose, T.M. &Bruce, A.G. (1991), Oncostatin M is a member of a cytokine family that includes leukemiainhibitory factor, granulocyte colony-stimulating factor, and interleukin-6. Proc. nat. Acud. Sci. (Wash.), 88, 8641-8645. Rosenberg, Z.F. & Fauci, A.S. (1990), Immunopathogenic mechanisms of HIV infection : cytokine induction of HIV expression. Immunol. Today, 11, 176-180. Sander, B., Andersson, J. & Andersson, U. (1991). As-

Growth

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sessment of cytokines by immunofluorescence and the paraformaldehyde-saponin procedure. Immunol. Rev., 119, 65-93. Tsunetsugu-Yokota, Y. & Honda, M. (1990), Effect of cytokines on HIV release and IL-2 receptor alpha expression in monocytic cell lines. J. AIDS, 3, 511-516. Von Briesen, H., von Mallinckrodt, C., Esser, R., Muller, S., Becker, K., Rubsamen-Waigmann, H. & Andreesen, R. (1991), Effect of cytokines and lipopolysaccharides on HIV infection of human macrophages. Res. Viral., 142, 197-204.

of IL6 and antitumour

effects

M. Revel Weizmann

Direct and indirect

antitumour

Institute

of Science, Rehovot

effects

Cytokines which combine direct action on tumour cell growth and differentiation with indirect actions on host immune and other defences are the best candidates for antitumour potential in vivo. The indirect effects appear essential, as shown for interferons which have antitumour activity even on malignant cells resistant to their growth-inhibitory effects (Gresser et al., 1990). The pleiotropic functions of IL6 in haematopoiesis, in immune and inflammatory responses, combined with growth inhibition on certain malignant cells, led us to propose an antitumour potential for this cytokine (Revel et al., 1989). Indeed, IL6 could induce host defences against tumours because it (i) stimulates differentiated functions of B and T lymphocytes, antibody production and cytotoxic effecters, (ii) enhances all haematopoiesis at the stem cell level, (iii) promotes maturation of myeloid lineages, monocytes, granulocytes, megakaryocytes (with increased platelet production), (iv) induces complement in various tissues, and (v) induces liver acute phase proteins including antiproteases which may restrict tumour invasion (reviewed in Kishimoto, 1989; Revel, 1989). Since these host effects reflect the stimulation of growth and activity of some haematopoietic and immune cells, it is not surprising that (like other cytokines,

(Israel)

e.g. TNF), IL6 has been seen to exert the opposite effects on growth of various normal and malignant cells (table I). Thus, IL6 promotes growth and may be an autocrine growth factor in a number of plasmacytomas and myelomas (Kawano et al., 1988), EBV-transformed B lymphocytes (Tosato el al., 1990), several T- and B-cell lymphomas (Yee et al., 1989), Kaposi-sarcoma-derived cells (Miles et al., 1990) and psoriatic keratinocytes (Grossman et al., 1989). On the other hand, IL6 acts as a growth inhibitor and differentiation factor for a number of carcinoma and leukaemia cell lines, which suggested it could in some cases have direct anti-tumour activities (Chen et al., 1988a). Growth-inhibitory cultures Human

effects of IL6 on malignant

breast and ovarian carcinoma

cell

cells

Dose-dependent growth inhibition by IL6 is observed in a number of human breast carcinoma cell lines: ductal carcinomas T47D, ZR-75-1 and ZR-75-30, adenocarcinomas SK-BR-3 and MCF-7 (Chen et al., 1988a, 1991; Tamm ef al., 1989, 1991; Brown et al., 1991). On T47D cell clones, growth of colonies from sparsely seeded cells can be fully in-