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immunologic changes observed following injury have been addressed only recently. We have found that the concentration of PGE in the sera of patients with major burns is generally high (1 000-3 000 pg m1-1 compared with less than 100 pg rnl- ~in normal subjects) and that these sera often significantly suppress in-vitro lymphocyte responsiveness 23. This suppression can,often be reduced by delipidation of the sera, or by the addition of monospecific anti-PGE 2 (Ref. 23). Albumin binds PGE and may also have a role in PGs suppressive activity. Burn patients generally have a profound deficit of albumin. When suppressive burn sera are fractionated by gel filtration, the active material co-elutes with low molecular weight peptides, some of which we have identified as albumin fragments. We are currently investigating the possible participation of these fragments in the stabilization of PG in the sera and their possible contribution to suppressive activity. The literature is replete which descriptions of low molecular weight suppressive peptides associated with burn injury, surgical trauma, cancer, and other medical problems. It is possible that many of these suppressor substances owe their activity to associated PGs. [:]1 Acknowledgement Special thanks to Dr Alan Winkelstein, Professor of Medicine,
University of Pittsburgh School of Medicine, for his review of the manuscript and helpful suggestions. References 1 Zurier, R. B. (1982) in: Prostaglandins (Lee, J. B., ed.), pp. 91-112,
Elsevier, New York 2 Crunkhorn, P. and Willis, A. L. (1971) Br. J. Phaemacol. 41,507-512 3 Weissman, G.(1980) CurrentConcepts:ProstaglandinsinAcutelnflamrrultion, pp. 1-14, Upjohn Co., Kalamazoo 4 Penneys, N. S. (1980) Current Concepts: Prostaglandins and the Skin, pp. 11-17, Upjohn Co., Kalamazoo 5 Issekutz, A. C. and Movat, H. Z. (1982) Am. J. Pathol. 107,300-309 6 Rivkin, I., Rosenblatt, J. and Becker, E. L. (1975)J. lmmunol. 115, 1126-1134 7 Till, G., Kownatzki, E., Seitz, M. and Gemsa, D. (1979) Clin. hnmunol. Immunopathol. 12, 111-118 8 Peredes, J. M. and Weiss, S. J. (1982)J. Biol. Chem. 257, 2738-2740 9 Bankhurst, A. D., Hastain, E., Goodwin, J. S. and Peake, G. T. (1981) J. Lab. Clin. Med. 97, 179-186 10 Snider, M. E., FerteI, R. H. and Zwilling, B. S. (1982) Cell. Immunol. 74, 234-242 11 Gemsa, D., Seitz, M., Kramer, W., Till, G. and Resch, K. (1978)J. Immunol. 120, I187-1194 12 Cahill, J. and Hopper, K. E. (1982) Cell. Immunol. 67,229-240 13 Pelus, L. M. (1982)J. Ch'n. Invest. 70, 568-578 14 Ferraris, V. A. and DeRubertis, F. R. (1974)J. Clin. Invest. 54,378 386 15 Dy, M., Astoin, M., Rigaud, M. and Hamburger, J. (1980) Eur. ,]. ImmunoL 10, 121 126 16 Anderson, C. B., Jaffee, B. M. and C-raft, R. J. (1977) Transplantation 23, 444 447 17 Ziegler, J. L. (1982) Current Concepts: Cancer and the Prostaglandins, pp. 15-22, Upjohn Co., Kalamazoo 18 Goodwin, J. S. andWebb, D. R. (1980) Clin. lmmunol. Immunopathol. 15, 106-122 19 Kaneene, J. M. B., Anderson, R. K., Johnson, D. W. and Muscoplat, C. C. (1978) Infect. Immun. 22, 486-491 20 Balch, C. M., Dougherty, P. A. and Tilden, A. B. (1982)Ann. Su N, 196, 645-650 21 Blotman, F., Poubelle, P., Chalntreuil, J., Damon, M., Flandre, O., DePaulet, A. C. and Simon, L. (1982) Int. J. Immunophaemacol. 4, 119-125 22 Arturson, M. G. (1983)in: Traumatic Injury: Infection and Other Immunologic Sequelae (Ninnemann, J. L., ed.), pp. 57-78, University Park Press, Baltimore 23 Ninnemann, J. L. and Stoekland, A. E. (1984)J. Trauma 24, 201-207
Prostaglandin regulation of B-lymphocyte function Nigel D. Staite* and Gabriel S. Panayit The local production of prostaglandins (PGs) in tissues by monocytes, polymorphonuclear leucocytes, endothelial cells and platelets, and their rapid degradation, gives PGs an ideal opportunity for the selective regulation of inflammatory and immune responses. Much is known about the PG regulation of monocyte and T-cellfunction 1-~but our knowledge of PGmediated regulation of B-lymphocyte function is still very poor, with many apparent contradictions in the literature. Here Nigel Staite and Gabriel Panayi discuss the indirect and direct effects OfPGs on B-lymphocyte function with particular emphasis on the regulation of human lymphoeytes, acknowledging that most of what is known was learned from animal studies. PGs and antigen-speciflc antibody responses is increased by in-vivo administration of 1 pg of PGE2, The i.v. injection of sheep erythrocytes (SRBC) in mice PGFI, or PGF2~ (Ref. 6). Experiments in vitro show that results-2 min later in an increase in PGF2~ levels in the treatment of cell cultures with cyclo-oxygenase inhibitors spleen from 30 to 600 pg/mg -~ protein ~. Intravenous increases the secondary anti-SRBC response of primed soluble antigen, such as bovine ),-globulin (BGG) also murine spleen cells 7 and support the hypothesis that PGs stimulates PG production but more slowly, peaking after suppress immunoglobulin production in the mouse. 2 h. Antigen-induced PG production can be inhibited In rats, the spleen contains a phagocytic, adherent, with drugs such as indometacin given 24 h before injecsuppressor cell with macrophage-like characteristics. tion of SRBC. Furthermore, indometacin given before Their removal increases the secondary PFC response of SRBC increases the primary murine anti-SRBC spleen cells to heterologous erythrocytes a'9. 'Their supresponse in vivo 4'5, which suggests that PGs suppress antipressive effect seems to be mediated via PG since indobody responses in vivo. There is, however , conflicting metacin, aspirin and RO3-1314 (a compound with a evidence that the secondary plaque-forming cell response selective inhibitory action on cyclo-oxygenase) all in(PFC) of 5-6 week old dd/Y mice immunized with SRBC crease PFC responses in cultures of unseparated spleen cells - an effect abrogated by exogenous PGE 2 (Ref. 9). *Department of Medicine, Rheumatology Section, 14-169 Pretreatment of rats with 500/ag of PGEI subcutaneously Human Sciences, University of Minnesota, Minneapolis, twice a day for 14 days also suppresses primary antiMN55455, USA. SRBC responses in-vivo 1°. Thus, in both the rat and mouse antibody responses to SRBC measured by PFC *Depts of Medicine, Guy's Hospital Medical School, Guy's Hospital, London SE1 9RT, UK. are inhibited by PGs. © 1984,ElsevierSciencePublishersB.V., Amsterdam 0167 4919/84/$02.(Yd
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In rabbits, however, PGs have different effects. Primed lymph-node cells can be induced to produce anti-dinitrophenol (DNP) or anti-keyhole limpet haemocyanin (KLH) by stimulation with anti-immunoglobulin (antiIg) for 24 h followed by culture in lymphokine-containing medium for 6 days. PGE1, added during stimulation with anti-Ig, increases the production of anti-DNP antibody ~1. This effect can be mimicked with dibutyryl cAMP (Ref. 11). PGE1 or PGE 2 increases the secondary in-vitro response to K L H whilst PGF~ has no effect. Indometacin suppresses antibody production but not if PGE~ or PGE2 is added at the same time a2' The effect of PGs on human primary and secondary antibody responses in vivo is unclear. In one study, indometacin (100 mg per day) given to healthy subjects immunized with A-Victoria and A-New Jersey influenza viruses, increased antibody titres to the A-Victoria strain but not to A-New Jersey. Since the subjects had been previously exposed to A-Victoria but not A-New Jersey, these results were taken to show that PGs are involved in the suppression of in-vivo secondary antibody responses. The increase in antibody titres in indometacin-treated subjects was, however, modest and only marginally significant 13.A second study showed that indometacin given to healthy elderly people had no effect on the antibody response to pneumococcal vaccinC *. More studies are needed.
PG regulation of mitogen-induced Ig production H u m a n B lymphocytes will secrete Igs in vitro when stimulated with a B-cell activator, such as pokeweed mitogen (PWM). While investigating the relationship ofintracellular cAMP levels to Ig production, Smith et al. 15 showed that PGE1 had little effect on PWM-stimulated IgG or IgA production from human tonsillar cells, but Ig production was low and the concentrations of PGE 1used were high (10 -4-10-6 M). Morito et al. 16 concluded that PG had no significant physiological role in the regulation of Ig production because only high (10-5 M) concentrations of PG influenced Ig synthesis (suppression was observed). Studies have often been criticized because the pharmacological concentrations of PG used (up to 10 -6 M) are not physiological. One drawback to studies of this sort is the extent of endogenous PG synthesis, and this may be why the effects of exogenous PG are seen only at high concentrations. Furthermore, at sites of inflammation there are undoubtedly high local concentrations of PG and lymphocytes may be in intimate contact with PG-secreting monocytes. Responses by lymphocytes to PG concentrations of 10 - 6_10 8M perhaps therefore do reflect events in l)io0.
Rather than add PGs to cultures one can examine the effects ofa cyclo-oxygenase inhibitor. Our published data support the suggestion that PGs are required for PWMdriven Ig synthesis from human mononuclear cells, since indometacin (10-6-10 -8 M) inhibits IgG and IgM production in healthy subjects 17. This effect, confirmed by Ceuppens and Goodwin TM, can be reproduced with several cyclo-oxygenase inhibitors. Indometacin is not cytotoxic at these concentrations and has no effect on PWM-induced proliferation. Its inhibitory effect can be
Immunology Today, vol. 5, No. 6, 1984
antagonized with exogenous PGE 2 (10-6-10 -8 M) but, interestingly, less potently on IgM production than on IgG production 17. PGE 2 stimulates IgG synthesis and, more weakly, IgM production. PGE 1 added to indometacin-treated cultures also stimulates in-vitro IgM production 19. This raises the possibility that prostanoids other than PGE 2 are more important in the regulation of IgG synthesis. The stimulatory effect of PGE 2 can also be seen in the augmented PFC response of human mononuclear cells to staphylococcal protein A (Ref. 20) and the faster differentiation of human plasma cells stimulated with P W M 21. The requirements for PGs in PWM-driven Ig synthesis suggest that PG-mediated immunoregulation may be very similar in rabbits and humans.
Mechanisms of PG-mediated immunoregulation In simple terms, PG regulation of Ig production could be thought of as the interaction of a PG-secreting monocyte with a PG-receptor-bearing T cell which regulates the extent of B-cell growth and differentiation into Ig secreting cells. The function of the PG-receptor-bearing T cell and its interaction with other T cells are unknown but there may be species differences. Webb and his colleagues have characterized two PGinduced suppressor factors produced by mouse T cells: PITS a and PITS/3 (Ref. 22). PITS/3 has a wide spectrum of suppressive actions, diminishing both phytohaemaglutinin (PHA)- and lipopolysaccharide (LPS)-induced blastogenesis, the one-way and two-way mixed lymphocyte reaction (MLR) and both T-cell-dependent and -independent antibody responses. PITS 13 is produced in response to allogeneic stimulation and exerts its effect during the first 2-4 h of culture. PGE 2 (but not PGF_= or other agents that increase cAMP) induces PITS proSuction 23. It is not yet clear whether PITS/3 acts directly on responding cells or via the induction o f T suppressor cells. In human cell cultures, PGs become effective shortly after P W M stimulation (within 24 h) and inhibition of PG synthesis is reflected in decreased Ig production after 11 days of culture 17. This involvement of PG in early immunoregulatory events is analogous to PG-dependent induction of cytotoxic and suppressor T lymphocytes within the first 24-48 h of culture 2,-26. The mechanism of action of PG in these cultures is far from clear. The ability ofPGE 2 to stimulate in-vitro Ig production depends on the presence of an OKT8 + ve suppressor cell 16. The PGE 2receptor-bearing T cell has Fc receptors for IgG (Ref. 27). If a human equivalent of murine PITS is produced, its target might be a suppressor T cell, since this would result in inhibition of suppressor-cell activity with a corresponding increase in Ig production. Circumstantial evidence in support of this hypothesis is the observation that the PGreceptor-bearing human T cell (the PITS-secreting cell?) has contrasuppressor characteristics since PG inhibits Con-A induction of suppressor cells whose effects can be assayed in the allogeneic one-way M L R (Ref. 28). These data are not without contradiction: there are two reports that PGs are required for Con-A activation of suppressor T cells 7'z6.However, the results of Orme and Shand 7were obtained with mouse cells, which respond differently to PGs. If murine cultures do not involve a PG-activated contra-suppressor cell, then the difference in results could
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be explained in terms of direct stimulation of Con-A activated suppressor T cells by PGs.
Direct effects of PGs on B lymphocytes The effects of PGs on the response of B lymphocytes to T-dependent antigens and mitogens are almost certainly largely mediated via the action of PG on T lymphocytes but PGs c a n also directly influence B lymphocytes. Antibody responses of murine spleen cells to two T-independent antigens, polyvinylpyrrolidone (PVP) and dinitrophenyl (DNP)-'Ficoll' are increased in the presence of prostaglandin synthetase inhibitors. This effect is most pronounced when PG synthesis is blocked 4-8 h after the addition of antigen 29. Stimulation of semi-solid cultures of human B lymphocytes with Staphylococcus aureus induces colony formation that is monocyte-dependent but can be suppressed by the addkion of excess monocytes. Addition of PGE~ and PGE2, but not PGF2~, suppresses colony growth ~°. This effect could be mediated by the action of PG on monocytes in these cultures but it is also possible that some B-cell phenotypes involved in colony formation might respond directly to PGs. PG regulation of other B-lymphocyte functions Administration of large numbers of SRBC to mice results in the generation of splenic B lymphocytes which, in syngeneic recipients, can induce antigen-specific suppressor T cells. These B-lymphocytes have been termed suppressor-inducer B cells. Indometacin given during the administration of SRBC, inhibits the generation of these cells - an effect not seen if PG synthesis is inhibited before, or more than 2 days after, priming with SRBC (Ref. 31). These results are analogous to the PGdependence of suppressor T-lymphocyte induction. Procarbazine, a powerful immunosuppressant, given 4 days prior to skin grafting increases graft survival in mice. Subcutaneous PGEI alone does not increase graft survival but PGE~ given for 20 days after procarbazine treatment prolongs skin graft survival for longer than procarbazine alone. This synergistic effect occurs after antigen sensitization and involves a decrease in the number of splenic complement-receptor-bearing cells. Since antibody production to Brucella abortus was not diminished in these animals, it is possible that procarbazine/PGEl treatment selectively suppresses cytotoxic B lymphocytes 32. PGs and antibody production in disease In many diseases, such as diffuse cutaneous leishmaniasis, Hodgkin's disease, 'atypical' mycobacteriosis and rheumatoid arthritis (RA), the proliferative response of mononuclear cells to a number of stimuli is abnormally low 33-36. In many cases responses can be partly restored to normal either by depletion of adherent 'suppressor' monocytes or by the addition of indometacin. Monocytederived PG therefore appears to suppress cellular proliferation in vitro, but the implication of this in vivo is unclear. Nevertheless, the hypothesis that PG-mediated immunoregulation is abnormal in certain diseases because of abnormal responsiveness to, or levels of, synthesis of PG is attractive, even if currently without strong evidence.
There have been few studies of the role of PG in the regulation of in vitro Ig synthesis in non-malignant disease. We have reported that the increased spontaneous in vitro Ig production by peripheral blood mononuclear cells from rheumatoid arthritis (RA) patients (including IgM-rheumatoid factor, IgM-RF) cannot be inhibited by indometacin 37and so is unlikely to be caused by increased PG production from these cells. In cultures from some RA patients, generally poor responders to PWM, PWMinduced Ig production is not inhibited by indometacin. In these patients, therefore, peripheral blood mononuclear cells may have progressed beyond the early immunoregulatory events involving PG, since indometacin exerts its inhibitory effect on Ig synthesis within the first 24 h of P W M stimulation 17. This raises the possibility that in RA, PG may play a significant part in the regulation ot lymphocyte activation in vivo. However, Ceuppens et al. have demonstrated that indometacin can inhibit PWMstimulated IgM-RF synthesis in vitro in both RA patients and healthy subjects selected for their ability to produce IgM-RF (Ref. 38) and that this may be a beneficial action of non-steroidal anti-inflammatory drugs in vivo. This apparent disagreement about the effects of indometacin on IgM-RF synthesis in RA patients may be explained by a difference in P W M responsiveness in the experimental groups studied. RA may resemble systemic lupus erythematosus (SLE), where PGE 2 has no effect on PWM-stimulated in vitro plasma-cell differentiation and indometacin fails to inhibit plasma cell formation in a proportion of individuals 21. In SLE, peripheral blood mononuclear cells may also have progressed beyond PGmediated immunoregulation. Our knowledge of the ways in which prostaglandins modulate humoral immunity is still increasing and our understanding of the cellular mechanisms involved will no doubt become clearer. PGs exert different effects in different animal species and these effects involve the modulation of both T cells and direct effects on B lymphocytes. The immunoregulatory role of PGs in other diseases is an intriguing area for future research. [~]
References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Pelus, L. M. and Strausser, H. R. (1977) Life Sci. 20, 903-914 Bray, M. A. (1980) Immunol. Today 1, 65-69 Stenson, W. F. and Parker, (3. W. (1980)J. Immunol. 125, l-5 Webb, D. R. and Osheroff, P. L. (1976)Proe. NatlAcad. Sci. USA 73, 1300-1304 Wehb, D. R. and Nowowiejski, I. (1977) Cell Immunol. 33, 1-10 Ishizuka, M., Takeuchi, T. and Umezawa, H. (1974) Experientia 30, 1207-1208 Orme, I. M. and Shand, F. L. (1981) Int. J. Immunopharmacol. 3, 15-19 Weiss, A. and Fitch, F. W. (1978)J. ImmunoL 120, 357-359 Matingly, J. A. and Kemp, J. D. (1979) Cell Immunol. 48, 195-200 Zurier, R. B. and Quagliata, F. (1971)Nature (London)234, 304-305 Kishimoto, T. and Ishizaka, K. (1976)J. Immunol. 116, 534--541 Gerblich, A. A. and Stavitsky, A. B. (1979) CeUlmmunoL 48, 318-328 Goodwin, J. S., Selinger, D. S., Messner, R. P. and Reed W. P (1978) Infect. Immun. 19, 430-433 Lafferty, W. P., Selinger, D. S., Schiffman, G. and Goodwin, J. S. (1981)~ ImrnunopharmacoL 3, 241-250 Smith, R. S., Sherman, N. A. and Coffey, R. G. (I974) Int. Arch. Allergy 47, 586-597 Morito, T., Bankhurst, A. D. and Williams, R. C. (1980) Prostaglandins 20, 383-390 Stake, N. D. and Panayi, G. S. (t982) Clin. Exp. Irnrnunol., 49, 115-122 Ceupens, J. L. and Goodwin, J. S. (1982) Cell. Immunol. 70, 41 54 Dunne, J. V., Fosse, B., Leung, T. and McKendry, R. J. (1981 i Prostanglandins Med. 6, 419-425
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20 Antonaci, S.,Jirillo, E., Montemur~o, P., Barbaro, L., Bonomo, L. and Fumarola, D. (1982) Prost. Leuk. in Med. 9, 295-300 21 Lydyard, P. M., Brostoff, J., Hudspith, B. N. and Parry, H. (1982) Immunol. Lett. 4, 113-6 22 Rogers, T, J., Nowowiejski, I. and Webb, D. R. (1980) CellImmunoL 50, 82-93 23 Rogers, T.J., Campbell, L., Calhoun, K., Nowowiejski, I. and Webb, D. R. (1982) Cell Immunol. 66, 269-276 24 Leung, K. H. and Michlich, E. (1980) Nature (London) 288, 597-600 25 Darrow, T. L. and Tomar, R. H. (1980) Cell Immunol. 56, 172-183 26 Fischer, A., Durandy, A. and Griscelli, C. (1981)J. Iramunol. 126, 1452-1455 27 Goodwin,J. S., Kaszubowski, P. A. and Williams, R. C. (1979)J. Exp. Med. 150, 1261-1264 28 Goodwin, J. S. et al. (1978)J. Clin. In~est. 62, 753-760 29 Zimecki, M. and Webb, D. R. (1976)J. Immunol. 117, 2158-2164 30 Whisler, R. L. and Newhouse, Y. G. (1982) Cell ImmunoL 69, 34-45
31 Shimamura, T., Hashimoto, K. and Sasaki, S. (1982) CelllmmunoL 69, 192-195 32 Quagliata, F., Lawrence, V. J. W. and Phillips-Quagliata,J. M. (1973) Cell ImmunoL 6, 457-465 33 Peterson, E. A., Neva, F. A., Oster, C. N. and Diaz, H. B. (1982) New Engl. J. Med. 306, 387-392 34 Goodwin, J. S., Messner, R. P., Bankhurst, A. D., Peake, G. T., Saiki, J. H. and Williams, R. C. (1977) New Engl. ,~ Med. 297,963-968 35 Mason, U. G., Greenberg, L. E., Yen, S. S. and Kikpatrick, C. H. (1982) Cell ImmunoL 71, 54-65 36 Wolinsky, S. I., Goodwin, J. s., Messner, R. P. and Williams, R. C. (1980) Clin, IrnmunoL andImmunopathoL 17, 31-37 37 Staite, N. D., Ganczakowski, M., Panayi, G. S. and Unger, A. (1982) Clin. Exp. ImrnunoL 52,535-542 38 Ceuppens, J. L., Rodriguez, M. A. and Goodwin, J. S. (1982)Lancet i, 528-530
Retinoids and in vivo immunity to transplantable tumours: a terra relatively incognita Miroslav Malkovsk~ and Peter B. Medawar Miroslav Malkovskj and Peter Medawar discuss here the role of retinoids in anti-tumour immunity in vivo with the intention of provoking a reassessment of the current status and potential of this topic. The# selection of results discussed is influenced by the belief that they may form a basis for a renaissance in the study of the biological functions of vitamin A. '1 have often had cause to feel that my hands are cleverer than my head. That is a crude way of characterizing the dialectics of experimentation. When it is going well, it is like a quiet conversation with Nature. One asks a question and gets an answer; then one asks the next question, and gets the next answer. An experiment is a device to make Nature speak intelligibly. After that one has only to listen.' GEORGEWALD
Vitamin A (retinol) and some of its derivatives (retinoids) support vital physiological functions in man and higher animals ~-3 and, by modifying carcinogenic processes, they can also act as potent anti-neoplastic agents 4-6. Moreover, retinoid substances often exert a regulatory influence on immune responses 7-1°. This provides a theoretical framework for the studies examining protective effects of retinoid substances against transplantable tumours. Quite often, however, inconsistent results have been reported, and sometimes no immunoregulatory effects were noted. Bollag ~ observed that retinoic acid given orally or intraperitoneally had no inhibitory effect on the following six transplantable tumours: Ehrlich solid carcinoma, Ehrlich ascites carcinoma, Crocker sarcoma 180 and leukemia L1210 in mice, and Walker 256 earcinosarcoma and uterus epithelioma T-8 (Guerin) in rats. The same author also demonstrated that an aromatic retinoic acid analog exerted no influence whatsoever on the growth of the above four murine transplantable tumours ~2. Felix et al. ~ showed that intraperitoneal pretreatment of BALB/c mice with retinyl palmitate did not protect challenged mice from a syngeneic transplanted methylcholanthrene-induced turnout of low immunogenicity and that intralesional treatment with retinyl palmitate was not significantly better than saline in curing the same tumour. Patek et al. ~ failed to demonstrate inhibition of tumour growth as a result of systemic retinoic acid injection in BALB/c mice
Clinical Research Centre, Harrow, Middlesex HA1 3UJ, UK.
transplanted with syngeneic fibrosarcomas A31.MA.4 and BNL1MEA.7R.1 (transformed in vitro with methylcholanthrene), a Kirsten murine sarcoma virusinduced sarcoma KA31 and a Moloney murine sarcoma virus-induced sarcoma MSV85.C1.3. Baron et al. 15 reported that retinoic acid treatment did not slow the growth ofP388 tumours in DBA/2 mice. Interpretation of these negative findings is difficult because the dose, timing, route of administration and pharmacological characteristics of the retinoid substance tested, and also the dose and immunogenicity of the tumour inoculum are all interacting variables which influence the experimental outcome. It is notable that treatments combining retinyl palmitate with cyclophosphamide 16, Bacillus CalmetteGudrin 17'18 or Corynebacterium parvum 19 caused tumour inhibition suggesting, albeit indirectly, that retinoid substances can activate or strengthen certain immune functions restricting the growth of tumours in vivo. In 1972, Tannock et al. 2° performed radiation dose response assays for two tumours and as an end-point considered the mean radiation dose yielding local tumour control in 50% of mice. Retinyl palmitate-treated mice required a lower dose of local, tumour-directed irradiation to eliminate an immunogenic fibrosarcoma than control mice not receiving retinyl palmitate. This effect of retinyl palmitate was abrogated by immune suppression of mice using whole-body irradiation and there was no effect of retinyl palmitate against a mammary carcinoma of very weak immunogenicity. These results suggest that retinyl palmitate may act through a mechanism of immunopotentiation.
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immunologic changes observed following injury have been addressed only recently. We have found that the concentration of PGE in the sera of patients with major burns is generally high (1 000-3 000 pg m1-1 compared with less than 100 pg rnl- ~in normal subjects) and that these sera often significantly suppress in-vitro lymphocyte responsiveness 23. This suppression can,often be reduced by delipidation of the sera, or by the addition of monospecific anti-PGE 2 (Ref. 23). Albumin binds PGE and may also have a role in PGs suppressive activity. Burn patients generally have a profound deficit of albumin. When suppressive burn sera are fractionated by gel filtration, the active material co-elutes with low molecular weight peptides, some of which we have identified as albumin fragments. We are currently investigating the possible participation of these fragments in the stabilization of PG in the sera and their possible contribution to suppressive activity. The literature is replete which descriptions of low molecular weight suppressive peptides associated with burn injury, surgical trauma, cancer, and other medical problems. It is possible that many of these suppressor substances owe their activity to associated PGs. [:]1 Acknowledgement Special thanks to Dr Alan Winkelstein, Professor of Medicine,
University of Pittsburgh School of Medicine, for his review of the manuscript and helpful suggestions. References 1 Zurier, R. B. (1982) in: Prostaglandins (Lee, J. B., ed.), pp. 91-112,
Elsevier, New York 2 Crunkhorn, P. and Willis, A. L. (1971) Br. J. Phaemacol. 41,507-512 3 Weissman, G.(1980) CurrentConcepts:ProstaglandinsinAcutelnflamrrultion, pp. 1-14, Upjohn Co., Kalamazoo 4 Penneys, N. S. (1980) Current Concepts: Prostaglandins and the Skin, pp. 11-17, Upjohn Co., Kalamazoo 5 Issekutz, A. C. and Movat, H. Z. (1982) Am. J. Pathol. 107,300-309 6 Rivkin, I., Rosenblatt, J. and Becker, E. L. (1975)J. lmmunol. 115, 1126-1134 7 Till, G., Kownatzki, E., Seitz, M. and Gemsa, D. (1979) Clin. hnmunol. Immunopathol. 12, 111-118 8 Peredes, J. M. and Weiss, S. J. (1982)J. Biol. Chem. 257, 2738-2740 9 Bankhurst, A. D., Hastain, E., Goodwin, J. S. and Peake, G. T. (1981) J. Lab. Clin. Med. 97, 179-186 10 Snider, M. E., FerteI, R. H. and Zwilling, B. S. (1982) Cell. Immunol. 74, 234-242 11 Gemsa, D., Seitz, M., Kramer, W., Till, G. and Resch, K. (1978)J. Immunol. 120, I187-1194 12 Cahill, J. and Hopper, K. E. (1982) Cell. Immunol. 67,229-240 13 Pelus, L. M. (1982)J. Ch'n. Invest. 70, 568-578 14 Ferraris, V. A. and DeRubertis, F. R. (1974)J. Clin. Invest. 54,378 386 15 Dy, M., Astoin, M., Rigaud, M. and Hamburger, J. (1980) Eur. ,]. ImmunoL 10, 121 126 16 Anderson, C. B., Jaffee, B. M. and C-raft, R. J. (1977) Transplantation 23, 444 447 17 Ziegler, J. L. (1982) Current Concepts: Cancer and the Prostaglandins, pp. 15-22, Upjohn Co., Kalamazoo 18 Goodwin, J. S. andWebb, D. R. (1980) Clin. lmmunol. Immunopathol. 15, 106-122 19 Kaneene, J. M. B., Anderson, R. K., Johnson, D. W. and Muscoplat, C. C. (1978) Infect. Immun. 22, 486-491 20 Balch, C. M., Dougherty, P. A. and Tilden, A. B. (1982)Ann. Su N, 196, 645-650 21 Blotman, F., Poubelle, P., Chalntreuil, J., Damon, M., Flandre, O., DePaulet, A. C. and Simon, L. (1982) Int. J. Immunophaemacol. 4, 119-125 22 Arturson, M. G. (1983)in: Traumatic Injury: Infection and Other Immunologic Sequelae (Ninnemann, J. L., ed.), pp. 57-78, University Park Press, Baltimore 23 Ninnemann, J. L. and Stoekland, A. E. (1984)J. Trauma 24, 201-207
Prostaglandin regulation of B-lymphocyte function Nigel D. Staite* and Gabriel S. Panayit The local production of prostaglandins (PGs) in tissues by monocytes, polymorphonuclear leucocytes, endothelial cells and platelets, and their rapid degradation, gives PGs an ideal opportunity for the selective regulation of inflammatory and immune responses. Much is known about the PG regulation of monocyte and T-cellfunction 1-~but our knowledge of PGmediated regulation of B-lymphocyte function is still very poor, with many apparent contradictions in the literature. Here Nigel Staite and Gabriel Panayi discuss the indirect and direct effects OfPGs on B-lymphocyte function with particular emphasis on the regulation of human lymphoeytes, acknowledging that most of what is known was learned from animal studies. PGs and antigen-speciflc antibody responses is increased by in-vivo administration of 1 pg of PGE2, The i.v. injection of sheep erythrocytes (SRBC) in mice PGFI, or PGF2~ (Ref. 6). Experiments in vitro show that results-2 min later in an increase in PGF2~ levels in the treatment of cell cultures with cyclo-oxygenase inhibitors spleen from 30 to 600 pg/mg -~ protein ~. Intravenous increases the secondary anti-SRBC response of primed soluble antigen, such as bovine ),-globulin (BGG) also murine spleen cells 7 and support the hypothesis that PGs stimulates PG production but more slowly, peaking after suppress immunoglobulin production in the mouse. 2 h. Antigen-induced PG production can be inhibited In rats, the spleen contains a phagocytic, adherent, with drugs such as indometacin given 24 h before injecsuppressor cell with macrophage-like characteristics. tion of SRBC. Furthermore, indometacin given before Their removal increases the secondary PFC response of SRBC increases the primary murine anti-SRBC spleen cells to heterologous erythrocytes a'9. 'Their supresponse in vivo 4'5, which suggests that PGs suppress antipressive effect seems to be mediated via PG since indobody responses in vivo. There is, however , conflicting metacin, aspirin and RO3-1314 (a compound with a evidence that the secondary plaque-forming cell response selective inhibitory action on cyclo-oxygenase) all in(PFC) of 5-6 week old dd/Y mice immunized with SRBC crease PFC responses in cultures of unseparated spleen cells - an effect abrogated by exogenous PGE 2 (Ref. 9). *Department of Medicine, Rheumatology Section, 14-169 Pretreatment of rats with 500/ag of PGEI subcutaneously Human Sciences, University of Minnesota, Minneapolis, twice a day for 14 days also suppresses primary antiMN55455, USA. SRBC responses in-vivo 1°. Thus, in both the rat and mouse antibody responses to SRBC measured by PFC *Depts of Medicine, Guy's Hospital Medical School, Guy's Hospital, London SE1 9RT, UK. are inhibited by PGs. © 1984,ElsevierSciencePublishersB.V., Amsterdam 0167 4919/84/$02.(Yd
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In rabbits, however, PGs have different effects. Primed lymph-node cells can be induced to produce anti-dinitrophenol (DNP) or anti-keyhole limpet haemocyanin (KLH) by stimulation with anti-immunoglobulin (antiIg) for 24 h followed by culture in lymphokine-containing medium for 6 days. PGE1, added during stimulation with anti-Ig, increases the production of anti-DNP antibody ~1. This effect can be mimicked with dibutyryl cAMP (Ref. 11). PGE1 or PGE 2 increases the secondary in-vitro response to K L H whilst PGF~ has no effect. Indometacin suppresses antibody production but not if PGE~ or PGE2 is added at the same time a2' The effect of PGs on human primary and secondary antibody responses in vivo is unclear. In one study, indometacin (100 mg per day) given to healthy subjects immunized with A-Victoria and A-New Jersey influenza viruses, increased antibody titres to the A-Victoria strain but not to A-New Jersey. Since the subjects had been previously exposed to A-Victoria but not A-New Jersey, these results were taken to show that PGs are involved in the suppression of in-vivo secondary antibody responses. The increase in antibody titres in indometacin-treated subjects was, however, modest and only marginally significant 13.A second study showed that indometacin given to healthy elderly people had no effect on the antibody response to pneumococcal vaccinC *. More studies are needed.
PG regulation of mitogen-induced Ig production H u m a n B lymphocytes will secrete Igs in vitro when stimulated with a B-cell activator, such as pokeweed mitogen (PWM). While investigating the relationship ofintracellular cAMP levels to Ig production, Smith et al. 15 showed that PGE1 had little effect on PWM-stimulated IgG or IgA production from human tonsillar cells, but Ig production was low and the concentrations of PGE 1used were high (10 -4-10-6 M). Morito et al. 16 concluded that PG had no significant physiological role in the regulation of Ig production because only high (10-5 M) concentrations of PG influenced Ig synthesis (suppression was observed). Studies have often been criticized because the pharmacological concentrations of PG used (up to 10 -6 M) are not physiological. One drawback to studies of this sort is the extent of endogenous PG synthesis, and this may be why the effects of exogenous PG are seen only at high concentrations. Furthermore, at sites of inflammation there are undoubtedly high local concentrations of PG and lymphocytes may be in intimate contact with PG-secreting monocytes. Responses by lymphocytes to PG concentrations of 10 - 6_10 8M perhaps therefore do reflect events in l)io0.
Rather than add PGs to cultures one can examine the effects ofa cyclo-oxygenase inhibitor. Our published data support the suggestion that PGs are required for PWMdriven Ig synthesis from human mononuclear cells, since indometacin (10-6-10 -8 M) inhibits IgG and IgM production in healthy subjects 17. This effect, confirmed by Ceuppens and Goodwin TM, can be reproduced with several cyclo-oxygenase inhibitors. Indometacin is not cytotoxic at these concentrations and has no effect on PWM-induced proliferation. Its inhibitory effect can be
Immunology Today, vol. 5, No. 6, 1984
antagonized with exogenous PGE 2 (10-6-10 -8 M) but, interestingly, less potently on IgM production than on IgG production 17. PGE 2 stimulates IgG synthesis and, more weakly, IgM production. PGE 1 added to indometacin-treated cultures also stimulates in-vitro IgM production 19. This raises the possibility that prostanoids other than PGE 2 are more important in the regulation of IgG synthesis. The stimulatory effect of PGE 2 can also be seen in the augmented PFC response of human mononuclear cells to staphylococcal protein A (Ref. 20) and the faster differentiation of human plasma cells stimulated with P W M 21. The requirements for PGs in PWM-driven Ig synthesis suggest that PG-mediated immunoregulation may be very similar in rabbits and humans.
Mechanisms of PG-mediated immunoregulation In simple terms, PG regulation of Ig production could be thought of as the interaction of a PG-secreting monocyte with a PG-receptor-bearing T cell which regulates the extent of B-cell growth and differentiation into Ig secreting cells. The function of the PG-receptor-bearing T cell and its interaction with other T cells are unknown but there may be species differences. Webb and his colleagues have characterized two PGinduced suppressor factors produced by mouse T cells: PITS a and PITS/3 (Ref. 22). PITS/3 has a wide spectrum of suppressive actions, diminishing both phytohaemaglutinin (PHA)- and lipopolysaccharide (LPS)-induced blastogenesis, the one-way and two-way mixed lymphocyte reaction (MLR) and both T-cell-dependent and -independent antibody responses. PITS 13 is produced in response to allogeneic stimulation and exerts its effect during the first 2-4 h of culture. PGE 2 (but not PGF_= or other agents that increase cAMP) induces PITS proSuction 23. It is not yet clear whether PITS/3 acts directly on responding cells or via the induction o f T suppressor cells. In human cell cultures, PGs become effective shortly after P W M stimulation (within 24 h) and inhibition of PG synthesis is reflected in decreased Ig production after 11 days of culture 17. This involvement of PG in early immunoregulatory events is analogous to PG-dependent induction of cytotoxic and suppressor T lymphocytes within the first 24-48 h of culture 2,-26. The mechanism of action of PG in these cultures is far from clear. The ability ofPGE 2 to stimulate in-vitro Ig production depends on the presence of an OKT8 + ve suppressor cell 16. The PGE 2receptor-bearing T cell has Fc receptors for IgG (Ref. 27). If a human equivalent of murine PITS is produced, its target might be a suppressor T cell, since this would result in inhibition of suppressor-cell activity with a corresponding increase in Ig production. Circumstantial evidence in support of this hypothesis is the observation that the PGreceptor-bearing human T cell (the PITS-secreting cell?) has contrasuppressor characteristics since PG inhibits Con-A induction of suppressor cells whose effects can be assayed in the allogeneic one-way M L R (Ref. 28). These data are not without contradiction: there are two reports that PGs are required for Con-A activation of suppressor T cells 7'z6.However, the results of Orme and Shand 7were obtained with mouse cells, which respond differently to PGs. If murine cultures do not involve a PG-activated contra-suppressor cell, then the difference in results could
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be explained in terms of direct stimulation of Con-A activated suppressor T cells by PGs.
Direct effects of PGs on B lymphocytes The effects of PGs on the response of B lymphocytes to T-dependent antigens and mitogens are almost certainly largely mediated via the action of PG on T lymphocytes but PGs c a n also directly influence B lymphocytes. Antibody responses of murine spleen cells to two T-independent antigens, polyvinylpyrrolidone (PVP) and dinitrophenyl (DNP)-'Ficoll' are increased in the presence of prostaglandin synthetase inhibitors. This effect is most pronounced when PG synthesis is blocked 4-8 h after the addition of antigen 29. Stimulation of semi-solid cultures of human B lymphocytes with Staphylococcus aureus induces colony formation that is monocyte-dependent but can be suppressed by the addkion of excess monocytes. Addition of PGE~ and PGE2, but not PGF2~, suppresses colony growth ~°. This effect could be mediated by the action of PG on monocytes in these cultures but it is also possible that some B-cell phenotypes involved in colony formation might respond directly to PGs. PG regulation of other B-lymphocyte functions Administration of large numbers of SRBC to mice results in the generation of splenic B lymphocytes which, in syngeneic recipients, can induce antigen-specific suppressor T cells. These B-lymphocytes have been termed suppressor-inducer B cells. Indometacin given during the administration of SRBC, inhibits the generation of these cells - an effect not seen if PG synthesis is inhibited before, or more than 2 days after, priming with SRBC (Ref. 31). These results are analogous to the PGdependence of suppressor T-lymphocyte induction. Procarbazine, a powerful immunosuppressant, given 4 days prior to skin grafting increases graft survival in mice. Subcutaneous PGEI alone does not increase graft survival but PGE~ given for 20 days after procarbazine treatment prolongs skin graft survival for longer than procarbazine alone. This synergistic effect occurs after antigen sensitization and involves a decrease in the number of splenic complement-receptor-bearing cells. Since antibody production to Brucella abortus was not diminished in these animals, it is possible that procarbazine/PGEl treatment selectively suppresses cytotoxic B lymphocytes 32. PGs and antibody production in disease In many diseases, such as diffuse cutaneous leishmaniasis, Hodgkin's disease, 'atypical' mycobacteriosis and rheumatoid arthritis (RA), the proliferative response of mononuclear cells to a number of stimuli is abnormally low 33-36. In many cases responses can be partly restored to normal either by depletion of adherent 'suppressor' monocytes or by the addition of indometacin. Monocytederived PG therefore appears to suppress cellular proliferation in vitro, but the implication of this in vivo is unclear. Nevertheless, the hypothesis that PG-mediated immunoregulation is abnormal in certain diseases because of abnormal responsiveness to, or levels of, synthesis of PG is attractive, even if currently without strong evidence.
There have been few studies of the role of PG in the regulation of in vitro Ig synthesis in non-malignant disease. We have reported that the increased spontaneous in vitro Ig production by peripheral blood mononuclear cells from rheumatoid arthritis (RA) patients (including IgM-rheumatoid factor, IgM-RF) cannot be inhibited by indometacin 37and so is unlikely to be caused by increased PG production from these cells. In cultures from some RA patients, generally poor responders to PWM, PWMinduced Ig production is not inhibited by indometacin. In these patients, therefore, peripheral blood mononuclear cells may have progressed beyond the early immunoregulatory events involving PG, since indometacin exerts its inhibitory effect on Ig synthesis within the first 24 h of P W M stimulation 17. This raises the possibility that in RA, PG may play a significant part in the regulation ot lymphocyte activation in vivo. However, Ceuppens et al. have demonstrated that indometacin can inhibit PWMstimulated IgM-RF synthesis in vitro in both RA patients and healthy subjects selected for their ability to produce IgM-RF (Ref. 38) and that this may be a beneficial action of non-steroidal anti-inflammatory drugs in vivo. This apparent disagreement about the effects of indometacin on IgM-RF synthesis in RA patients may be explained by a difference in P W M responsiveness in the experimental groups studied. RA may resemble systemic lupus erythematosus (SLE), where PGE 2 has no effect on PWM-stimulated in vitro plasma-cell differentiation and indometacin fails to inhibit plasma cell formation in a proportion of individuals 21. In SLE, peripheral blood mononuclear cells may also have progressed beyond PGmediated immunoregulation. Our knowledge of the ways in which prostaglandins modulate humoral immunity is still increasing and our understanding of the cellular mechanisms involved will no doubt become clearer. PGs exert different effects in different animal species and these effects involve the modulation of both T cells and direct effects on B lymphocytes. The immunoregulatory role of PGs in other diseases is an intriguing area for future research. [~]
References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Pelus, L. M. and Strausser, H. R. (1977) Life Sci. 20, 903-914 Bray, M. A. (1980) Immunol. Today 1, 65-69 Stenson, W. F. and Parker, (3. W. (1980)J. Immunol. 125, l-5 Webb, D. R. and Osheroff, P. L. (1976)Proe. NatlAcad. Sci. USA 73, 1300-1304 Wehb, D. R. and Nowowiejski, I. (1977) Cell Immunol. 33, 1-10 Ishizuka, M., Takeuchi, T. and Umezawa, H. (1974) Experientia 30, 1207-1208 Orme, I. M. and Shand, F. L. (1981) Int. J. Immunopharmacol. 3, 15-19 Weiss, A. and Fitch, F. W. (1978)J. ImmunoL 120, 357-359 Matingly, J. A. and Kemp, J. D. (1979) Cell Immunol. 48, 195-200 Zurier, R. B. and Quagliata, F. (1971)Nature (London)234, 304-305 Kishimoto, T. and Ishizaka, K. (1976)J. Immunol. 116, 534--541 Gerblich, A. A. and Stavitsky, A. B. (1979) CeUlmmunoL 48, 318-328 Goodwin, J. S., Selinger, D. S., Messner, R. P. and Reed W. P (1978) Infect. Immun. 19, 430-433 Lafferty, W. P., Selinger, D. S., Schiffman, G. and Goodwin, J. S. (1981)~ ImrnunopharmacoL 3, 241-250 Smith, R. S., Sherman, N. A. and Coffey, R. G. (I974) Int. Arch. Allergy 47, 586-597 Morito, T., Bankhurst, A. D. and Williams, R. C. (1980) Prostaglandins 20, 383-390 Stake, N. D. and Panayi, G. S. (t982) Clin. Exp. Irnrnunol., 49, 115-122 Ceupens, J. L. and Goodwin, J. S. (1982) Cell. Immunol. 70, 41 54 Dunne, J. V., Fosse, B., Leung, T. and McKendry, R. J. (1981 i Prostanglandins Med. 6, 419-425
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20 Antonaci, S.,Jirillo, E., Montemur~o, P., Barbaro, L., Bonomo, L. and Fumarola, D. (1982) Prost. Leuk. in Med. 9, 295-300 21 Lydyard, P. M., Brostoff, J., Hudspith, B. N. and Parry, H. (1982) Immunol. Lett. 4, 113-6 22 Rogers, T, J., Nowowiejski, I. and Webb, D. R. (1980) CellImmunoL 50, 82-93 23 Rogers, T.J., Campbell, L., Calhoun, K., Nowowiejski, I. and Webb, D. R. (1982) Cell Immunol. 66, 269-276 24 Leung, K. H. and Michlich, E. (1980) Nature (London) 288, 597-600 25 Darrow, T. L. and Tomar, R. H. (1980) Cell Immunol. 56, 172-183 26 Fischer, A., Durandy, A. and Griscelli, C. (1981)J. Iramunol. 126, 1452-1455 27 Goodwin,J. S., Kaszubowski, P. A. and Williams, R. C. (1979)J. Exp. Med. 150, 1261-1264 28 Goodwin, J. S. et al. (1978)J. Clin. In~est. 62, 753-760 29 Zimecki, M. and Webb, D. R. (1976)J. Immunol. 117, 2158-2164 30 Whisler, R. L. and Newhouse, Y. G. (1982) Cell ImmunoL 69, 34-45
31 Shimamura, T., Hashimoto, K. and Sasaki, S. (1982) CelllmmunoL 69, 192-195 32 Quagliata, F., Lawrence, V. J. W. and Phillips-Quagliata,J. M. (1973) Cell ImmunoL 6, 457-465 33 Peterson, E. A., Neva, F. A., Oster, C. N. and Diaz, H. B. (1982) New Engl. J. Med. 306, 387-392 34 Goodwin, J. S., Messner, R. P., Bankhurst, A. D., Peake, G. T., Saiki, J. H. and Williams, R. C. (1977) New Engl. ,~ Med. 297,963-968 35 Mason, U. G., Greenberg, L. E., Yen, S. S. and Kikpatrick, C. H. (1982) Cell ImmunoL 71, 54-65 36 Wolinsky, S. I., Goodwin, J. s., Messner, R. P. and Williams, R. C. (1980) Clin, IrnmunoL andImmunopathoL 17, 31-37 37 Staite, N. D., Ganczakowski, M., Panayi, G. S. and Unger, A. (1982) Clin. Exp. ImrnunoL 52,535-542 38 Ceuppens, J. L., Rodriguez, M. A. and Goodwin, J. S. (1982)Lancet i, 528-530
Retinoids and in vivo immunity to transplantable tumours: a terra relatively incognita Miroslav Malkovsk~ and Peter B. Medawar Miroslav Malkovskj and Peter Medawar discuss here the role of retinoids in anti-tumour immunity in vivo with the intention of provoking a reassessment of the current status and potential of this topic. The# selection of results discussed is influenced by the belief that they may form a basis for a renaissance in the study of the biological functions of vitamin A. '1 have often had cause to feel that my hands are cleverer than my head. That is a crude way of characterizing the dialectics of experimentation. When it is going well, it is like a quiet conversation with Nature. One asks a question and gets an answer; then one asks the next question, and gets the next answer. An experiment is a device to make Nature speak intelligibly. After that one has only to listen.' GEORGEWALD
Vitamin A (retinol) and some of its derivatives (retinoids) support vital physiological functions in man and higher animals ~-3 and, by modifying carcinogenic processes, they can also act as potent anti-neoplastic agents 4-6. Moreover, retinoid substances often exert a regulatory influence on immune responses 7-1°. This provides a theoretical framework for the studies examining protective effects of retinoid substances against transplantable tumours. Quite often, however, inconsistent results have been reported, and sometimes no immunoregulatory effects were noted. Bollag ~ observed that retinoic acid given orally or intraperitoneally had no inhibitory effect on the following six transplantable tumours: Ehrlich solid carcinoma, Ehrlich ascites carcinoma, Crocker sarcoma 180 and leukemia L1210 in mice, and Walker 256 earcinosarcoma and uterus epithelioma T-8 (Guerin) in rats. The same author also demonstrated that an aromatic retinoic acid analog exerted no influence whatsoever on the growth of the above four murine transplantable tumours ~2. Felix et al. ~ showed that intraperitoneal pretreatment of BALB/c mice with retinyl palmitate did not protect challenged mice from a syngeneic transplanted methylcholanthrene-induced turnout of low immunogenicity and that intralesional treatment with retinyl palmitate was not significantly better than saline in curing the same tumour. Patek et al. ~ failed to demonstrate inhibition of tumour growth as a result of systemic retinoic acid injection in BALB/c mice
Clinical Research Centre, Harrow, Middlesex HA1 3UJ, UK.
transplanted with syngeneic fibrosarcomas A31.MA.4 and BNL1MEA.7R.1 (transformed in vitro with methylcholanthrene), a Kirsten murine sarcoma virusinduced sarcoma KA31 and a Moloney murine sarcoma virus-induced sarcoma MSV85.C1.3. Baron et al. 15 reported that retinoic acid treatment did not slow the growth ofP388 tumours in DBA/2 mice. Interpretation of these negative findings is difficult because the dose, timing, route of administration and pharmacological characteristics of the retinoid substance tested, and also the dose and immunogenicity of the tumour inoculum are all interacting variables which influence the experimental outcome. It is notable that treatments combining retinyl palmitate with cyclophosphamide 16, Bacillus CalmetteGudrin 17'18 or Corynebacterium parvum 19 caused tumour inhibition suggesting, albeit indirectly, that retinoid substances can activate or strengthen certain immune functions restricting the growth of tumours in vivo. In 1972, Tannock et al. 2° performed radiation dose response assays for two tumours and as an end-point considered the mean radiation dose yielding local tumour control in 50% of mice. Retinyl palmitate-treated mice required a lower dose of local, tumour-directed irradiation to eliminate an immunogenic fibrosarcoma than control mice not receiving retinyl palmitate. This effect of retinyl palmitate was abrogated by immune suppression of mice using whole-body irradiation and there was no effect of retinyl palmitate against a mammary carcinoma of very weak immunogenicity. These results suggest that retinyl palmitate may act through a mechanism of immunopotentiation.
