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idiotype interaction may permit therapeutic manipulation are neurobiology and hormone-receptor modulation. The receptors on nerve cells or hormone-sensitive tissues can be targets for recognition by anti-receptor antibodies. Autoantibodies against insulin receptor, acetylcholine receptor, and fi-adrenergic receptors 32-3~are thought to be related directly or indirectly to some forms of diabetes, myasthenia gravis, and heart disease. Studies with such anti-receptor antibodies may provide information on the mechanism of receptor function and insight into control circuits that may permit regulation of these autoimmune diseases.

References 1 Roitt, I., Male, D. K., Guarnotta, G., deCarvalho, L. P., Cooke, A., Hay, F. C., Lydyard, P. M., Thanavala, Y. and Ivanyi, J. (1981)Lancet i, 1041 2 Rowley, D. A., K6hler, H. and Cowan, J. D. (1980) Contemp. Top. Immunobiol. 9, 205 3 Eichmann, K. (1978)Adv. Immunol. 26, 195 4 Jerne, N. K. (1974) Ann. Immunol. (Paris) 125C, 375 5 Cosenza, H. and K6hler, H. (1972) Proc. NatlAcad. Sci. USA 69, 2701 6 Hart, D. A., Wang, A. L., Pawlak, L. L. and Nisonoff, A. (1972)J. Exp. Med. 135, 1293 7 Binz, H. and Wigzell, H. (1976),]. Exp. Med. 142, 197 8 Julius, M. H., Cosenza, H. and Augustin, A. A. (1977) Nature (London) 267, 437 9 Eichmann, K. (1974) Eur. ,f Immunol. 4, 296 10 Eichmann, K. and Rajewsky, K. (1975) Eur. J. Immunol. 5, 661

11 Jayaraman, S., Swierkosz, J. E. and Bellone, C. J. (1982)J. Exp. Med. 155, 641 12 Sy, M. S., Dietz, M. H., Germain, R. N., Benacerraf, B and Greene, M. I. (1980)J. Exp. Med. 151, 1183 13 Maney, A., Baecher, L. and Begley, D. (1975) lmmunochemistry 12, 551 14 MaUey, A., Begley, D. and Forsham, A. (1980) Int. Arch. Allergy Appl. Immunol. 62, 276 15 Brandt, C. J., Deppe, L. B. and Malley, A. (1981) Immunology 44, 373 16 Malley, A., Brandt, C. J. and Deppe, L. (1982) Immunology 45, 217 17 Malley, A., Begley, D. and Forsharn, A. (1977) lmmunol. Commun. 6,473 18 Kelsoe, G., Reth, M. and Rajewski, K. (1980) ImmunoL Rev. 52, 75 19 Malley, A. and Dresser, D. R. Immunology (in press) 20 Wysocki, L.J. and Sato, V. L. (1978) Proc. NatlAcad. Sd. USA 75, 2844 21 Maizels, R. M. and Dresser, D. W. (1977) Immunology 32, 793 22 Eichrnann, K. and Kindt, T.J. (1971)J. Exp. Med. 134, 532 23 Kunkel, H. G., Agnello, V., Joslin, F. G., Winchester, R.J. and Capra, J. D. (1973)J. Exp. med. 137, 331 24 Williams, R. C., Kunkel, H. G. and Capra, J. D. (1968) Science161,379 25 Kindt, T. J., Seide, R. K., Bokisch, V. A. and Kranse, R. M. (1973)J. Exp. Med. 138, 552 26 Pasquali, J. L., Fong, S., Tsoukas, C., Vaughan, J. H. and Carson, D. A. (1980)J. Clin. Invest. 66, 863 27 Malley, A. and Perlman, F. (1970)J. Allergy 45, 14 28 Malley, A. and Harris, R. L. (1967)J. lmmunol. 99, 825 29 Malley, A., Crossley, G., Baecher, L., Wilson, B.J., Perlman, F. and Burger, D. (1973) in ControlMechanisms in Hypersensitivi~(L. Goodfriend, ed.), p. 83, Marcel Dekker, Inc., New York 30 Fairchild, D. and Medley, A. (1975)J. ImrnunoL 115, 1533 31 Bach, M., Wittner, M., Levitt, D. and KiShler, H. (1981) Fed. Proc. Fed. Am. Soc. Exp. Biol. 40, 1007 32 Barr, R. S., Harrison, L. C., Muggeo, M., Gordon, P., Kahn, C. R. and Roth, J. (1979) Adv. Intern. Med. 24, 23 33 Lindstrom, J. (1979)Adv. Immunol. 27, 1 34 Fraser, C. M. and Venter, J. C. in Membrane, Receptorsand the Immune Response(Cohen, E. P. and K6hler, H., eds), Alan R. Liss, New York (in press)

Molecular mechanisms in tumor-cell killing by activated macrophages Dolph O. Adams* and Carl F. Nathant Macrophages kill tumor cells with and without the aid of antibody and evidence suggests that secreted cytotoxic substances are at work in each system. Here Dolph Adams and Carl Nathan discuss the likely involvement in both pathways of several such substances including cytolytic protease and hydrogen peroxide. T u m o r cells co-cultivated with macrophages are lysed in at least two distinct circumstances. The interaction may be slow and independent of antibody - macrophagemediated tumor cytotoxicity (MTC), which is selective for neoplastically transformed targets; or it may be rapid and require antibody, which gives specificity to the lysis - antibody-dependent, cell-mediated cytotoxicity (ADCC)'. Macrophages which have been activated (i.e. their efficiency oflysis considerably heightened) will act in either M T C or ADCC, though the tWO modes of activation are not always coincident~'3. The physiological basis of activation for M T C appears to be an increased capacity for capturing targets and for secreting lytic substancesL The basis of activation for ADCC, while apparently distinct from that of M T C , also appears to include increased secretion oflytic substances 5. *Departments of Pathology and Microbiology and Immunology, Duke University, Durham, NC 27710; and tDepartment of Cellular Physiology and Immur]ology, The Rockefeller University, New York, NY 10021, USA.

A popular hypothesis is that macrophages destroy tumor cells in both M T C and A D C C by secreting molecules that injure the neoplastic targets. Evidence to date indicates that cytotoxic molecules are secreted from macrophages in several distinct circumstances: (1) spontaneously (i.e. without the intentional addition or recognized presence of stimuli in the cultures); (2) in response to various biological or pharmacological stimuli, including ligand-receptor interactions; and (3) after the appropriate binding of cellular targets ~'2'6. Since macrophages secrete a large number of substances capable of producing target injury in isolation, emphasis is currently being placed on defining those actually responsible for mediating target cytolysis in M T C and in ADCC. A full consideration of the role of target contact in cytolysis falls beyond the scope of this review. The attachment of tumor cells to activated macrophages is mediated via Fc receptors in A D C C 5 and via a different mechanism, probably a receptor that recognizes constituents of the plasma membrane of tumor cells, in M T C 4. Adherence between macrophages and targets may have © 1983,El.~vierSciencePublishe~B.V., Ar~terdam 0167t~ 49191831501.00

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several functions in cytolysis, including selection of targets for destruction and triggering the release of lytic factors. In addition, the narrow cleft between activated macrophages and bound targets (20-100 A °) could provide a diffusion-limited space, where secreted molecules could be concentrated and protected from macromolecular inhibitors in the extracellular fluid7'8. Models of cytolysis, which proceed in two stages - an initial binding step followed by release oflytic effectors - have been proposed for both M T C and A D C C ~'~'9. The weight of evidence to date favors the necessity of target contact in both M T C and A D C C 1'2'4'9,but there is no evidence that mere contact by macrophages induces target injury, as has been proposed in models of T-cell-mediated lysisJ°. O n the other hand, macrophages can occasionally lyse targets without contacting them. The relevance of such observations is, however, open to question if the experiments are conducted under marginal culture conditions.

Potential mediators of cytolysis Macrophages secrete over 60 different substances H, several of which can injure tumor cells (Table I). Secretion of these products frequently varies with the state of activation of the macrophages and often depends upon a two-step regulatory mechanism. An initial priming signal prepares the macrophages for release of the substance, and a second triggering signal elicits actual release6. Susceptibility to a given mediator can vary widely among targets and with the same target, depending on cell density in culture and the type or amount of medium and serum components present ~. Furthermore, cytotoxic substances can interact with one another to produce augmented target damage (see below). Thus, production of target damage can be quite complex. Five general lines of evidence implicate a given mediator in cytolysis (Table II). First, release of the mediator can be correlated with the development of activation or with the cytolytic potential of the macrophages. Although such evidence is only correlative, forceful arguments can be so adduced - particularly if release of the mediator is specific. Second, inhibitors of the mediator can be examined for their effects on cytolysis by activated macrophages. If the inhibitor is specific for the mediator in question and is demonstrably not toxic to the macrophages, inhibition of cytolysis is particularly compelling. Failure to inhibit cytolysis, however, may not be equally informative, since inhibitors may not be effective at concentrations achieved in culture, and macromolecular inhibitors may not be able to enter the space between macrophages and bound targets 7'8. Third, genetic deficiencies in release of a mediator can be a powerful probe for analysing cytolysis. Obviously, the specificity and totality of the postulated deficit must be rigorously defined. Fourth, specific release of the mediator in response to target attachment, though not a requirement for its involvement, is further evidence. Fifth, target effects of the mediator can be compared with target effects produced by macrophages. Although again correlative, this type of evidence can be quite persuasive- particularly when a number of correlations are established. Failure of a tumor cell to be lysed by activated macrophages, however, could indicate resistance to recognition rather than

resistance to injury. All of these approaches have been employed to examine M T C and A D C C , and those mediators that have been studied in some detail are considered below. P o t e n t i a l mediators of m a c r o p h a g e - m e d i a t e d tumor

cytotoxicity Several mediators have now been extensively studied in regard to M T C , including protease(s), tumor necrosis factor (TNF), H202 and arginase. Activated murine macrophages secrete a novel serine protease of Mr ~ 40 x 103, which selectively lyses a wide variety of neoplastic targets 12. The cytolytic protease (CP) is potent (i.e. the 50% cytolytic concentration is approximately 1.0 x 10 9M);and its lytic interaction with tumor cells has several characteristics of an enzyme-substrate reaction 12'13. Operationally, C P resembles cytolytic substances described by Currie and Basham, Sharma and Piessens, and Reidarson et al. ~4-~7. Although the molecular relationship(s), if any, among these three cytolytic substances and CP are not yet defined, the cytolytic principal described by Reidarson et al. can be resolved by gel filtration into two peaks of M r ~ 60 x 103 a n d M r ~ 150 x 103, and can be blocked by inhibitors of serine proteases. The relationship of membrane-bound proteases to M T C has not yet been explored. Such membrane-bound proteases can effect cytolysis in other models ~8, and mononuclear phagocytes do possess membrane-bound proteases ~9'2°. Multiple lines of evidence have been adduced to incriminate CP in M T C *'~3.First, secretion of CP correlates closely with the expression and development of activation for cytolysis. For example, signals that push precursor macrophages (i.e. primed macrophages capable of binding tumor cells) to fully cytolytic macrophages correspond in type and dose to signals that trigger release of CP. The stoichiometry of secretion is also appropriate, in that one activated macrophage can secrete sufficient CP to lyse a minimum of 10-20 tumor cells. Second, low-molecularweight inhibitors of serine proteases, which effectively inhibit CP, inhibit M T C by up to 90% in a dosedependent fashion and do so by acting on the targetinjury stage of cytolysis. Third, macrophages selectively deficient in secretion of CP in response to endotoxin cannot complete M T C in response to endotoxin 4. Such macrophages do secrete CP and do complete M T C in response to an alternate second signal (for example, maleylated bovine serum albumin) 2~. Fourth, direct binding of tumor cells, though not of other cellular targets, to activated macrophages triggers selective secretion of CP 22. Fifth, the course of target death as monitored by release of 51Cr from neoplastic cells is similar, when target destruction is caused by either activated macrophages or by isolated CP (i.e. a slowly rising sigrnoidal curve peaking at 16-18 h) ~3. The mechanisms by which C P leads to target injury are not yet known. CP may be directly cytotoxic or may initiate a series of events with cytotoxic outcome, though it does not appear to require a co-factor from the tumor cells~3. Taken together, strong arguments can be adduced that CP is one major effector of macrophage-mediated tumor cytotoxicity. There is, however, no reason to suppose that it is the sole mediator.

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TABLE I. Secretory products of mononuclear phagocytes reported to damage tumor cells References Cytolytic protease H202 Arginase Tumor necrosis factor Cytotoxic factors Thymidine C3A Lysosomal enzymes Lysozyme Interferon

12 30 43 23 See Refs 12 and 56 for reviews 57 58 (cf. Ref. 59) 60, 61 62 63

M o n o n u c l e a r phagocytes secrete substances capable of producing massive necrosis of tumors in vivo ( T N F ) 23 27. T h e molecular character of T N F is as yet incompletely defined 25-2s. W h e n tested against highly sensitive L cells, macrophage supernatants having T N F activity contain multiple peaks ofcytolytic activity, including one fraction o f M r ~ 50 x l0 s and multiple fractions in the range of Mr 100-225 x 103 (Ref. 27). Recently, a n antiserum raised against intact supernatants containing T N F activity has been shown to inhibit the lytic activity of such supernatants a n d to inhibit M T C to a limited degree as well29. Delineation of the precise lytic substance(s) against which the antiserum is directed m a y provide valuable information about the mediator(s) of M T C . H y d r o g e n peroxide can rapidly lyse a variety of neoplastic cellss'3°. Target susceptibility to H202, however, varies widely (i.e. the 50% cytolytic concentration in a m b i e n t m e d i u m can range from ~ 10- 6M to ~ 10- 3M)5'31. T h e role for H202 in M T C is as yet incompletely resolved. O n one hand, activated macrophages are primed for secretion of H202 a n d release it when confronted with appropriate triggering agents 32. It has been further calculated that macrophages could create a concentration of greater than 10 2M H 2 0 2 in the space between macrophages a n d b o u n d targets, if there were no loss o f H 2 0 2by diffusion or catabolism 33. Catalase has been variously reported either to have no effect on M T C 3.-36or to inhibit M T C 37-39. C a u t i o n is warranted in interpreting either finding, since inhibition required large a m o u n t s of catalase, and macromolecules such as catalase m a y not be able to penetrate the space between macrophages and b o u n d targets (see Refs 4, 7). O n the other hand, anaerobiosis did not inhibit M T C appreciably in two studies' (Ref. 36; V. F r e e d m a n a n d S. Silverstein, unpublished observations). Thus, the currently available data imply that secretion of H202 is not sufficient to mediate target injury in M T C with a n u m b e r of types of target cells, although there may be some exceptions 37-39 which require further study. This conclusion by no means excludes a role for H202 in M T C because H202 m a y co-operate with other lytic effectors in producing target injury. Brief exposure of tumor cells to a non-lytic concentration of H202 (i.e. 10 6M or less) renders these targets susceptible to otherwise non-lytic concentrations of cytolytiCo protease 31 . Indeed, the interaction of C P a n d H202 is synergistic3L I n this regard, the direct interaction between tumor targets

and activated macrophages can trigger release of "~ 1 nmole of O2-M, a n a m o u n t sufficient to raise the concentration in the extracellular milieu to ,~ 10-6M (Ref. 34). Eosinophil peroxidase can also interact with H202 to a u g m e n t cytolysis of tumor cells4°. Specifically, tumor cells, whether natively susceptible or resistant to H202 are u p to 75 times more susceptible to H202 w h e n coated with eosinophil peroxidase t h a n their untreated counterparts. O f particular interest, eosinophil peroxidase renders t u m o r cells susceptible to rapid, spontaneous cytolysis by activated macrophages; and this lysis can be completely inhibited by low concentrations of catalase *°. This suggests that activated macrophages secrete small a m o u n t s of H 2 0 ~ spontaneously, even though this baseline secretion m a y be difficult to detect by current assays and m a y increase only marginally in the presence of tumor cells34. This a m o u n t of H202 could contribute to cytolysis in the presence ofcytolytic protease and mediate cytolysis in the presence of eosinophil peroxidase. The latter might be important in vivo when macrophages and eosinophils infiltrate tumors. It is also possible that H~O2 could interact with another lytic substance to increase lytic potency of the latte? 1. The high arginine requirement of neoplastically transformed cells, in comparison to non-transformed cells, makes them susceptible to deprivation of this essential a m i n o acid ~2. Since macrophages can secrete sufficient arginase to deplete cultures ofarginine, arginase has been proposed as a molecular mediator of M T C .3. Arginase, however, is secreted by inflammatory as well as activated macrophages, and secretion ofarginase does not correlate closely with activation for t u m o r cytotoxicity~-~. T h e principal evidence supporting a role for arginase in M T C is the observation that arginine can inhibit the destruction of neoplastic cells when cultured with activated TABLE II. Lines of evidence used to implicate a mediator in effecting cytolysisby macrophages (I) Circumstances of mediator release A. Spontaneous mediator release correlates with development and expression of activation for cytolysis B. Stimulated release of mediator correlates with stimulated expression of cytolysis C. Amount of mediator released is consistent with amount required for cytolysis (II) Effect of inhibitors Specific inhibitors of the mediator inhibit the target injury stage of cytolysis. (III) Effect of macrophage deficiency Macrophages deficient in release of the mediator cannot complete the target-injury stage of cytolysis (IV) Effect of target attachment on mediator release Bindingof targets via the appropriate receptor stimulates release of the mediator (V) Nature of target injury A. Target injury by the mediator resembles target injury by macrophages B. Target susceptibility/resistance to the mediator correlates with target susceptibility/resistance to lysis by macrophages C. Alterations of target susceptibility to the mediator correlate with alterations in resistance/susceptibility to lysis by macrophages

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macrophages +3'+?. Such demonstrations, on occasion, have depended on medium low in arginine or otherwise marginal culture conditions. Macrophage-mediated cytotoxicity has not been inhibited by arginine in several laboratories~'+8. Arginase secretion by macrophages may well effect kill of tumor cells in culture, but a role for arginase in macrophage-mediated tumor cytotoxicity remains to be established fully.

Potential mediators of ADCC The lytic mechanisms operative in A D C C appear to be distinct from those in M T C (for review, see Ref. 3). For example, BCG-elicited macrophages from C 3 H / H e J mice or BCG-activated macrophages from control mice held in culture overnight are both unable to complete the lytic step in M T C , but both are capable of mediating A D C C +9. Hydrogen peroxide currently appears to be a major mediator of A D C C on the basis of several lines of evidence 2'5. First, the ability of macrophages to secrete H202 correlates well with their ability to mediate A D C C . The stoichiometry of H20 z secretion vis-h-vis production of target lysis is discussed above. Second, A D C C can be inhibited by deprivation of oxygen, deprivation of glucose, or by addition of thioglycollate broth, a scavenger ofH202. Again, the inability ofcatalase to alter A D C C ? must be considered in the knowledge that the cleft between macrophages and bound targets may be diffusion limited. Third, engagement of Fc receptors on macrophages can trigger copious secretion of H202. Fourth, the time course of lysis in A D C C and lysis mediated by H202 are rapid and quite similar. Finally, inhibition of target defenses against H202 markedly potentiates the ability of macrophages to mediate A D C C s°. It is interesting to note that macrophages, which are deficient in completing M T C but which mediate A D C C effectively, secrete H202 copiously+9. Taken together, these lines of evidence strongly implicate HzO 2 as a major mediator o f A D C C . The possibility of other lytic mediators effecting A D C C has been raised. Anaerobiosis has not inhibited A D C C completely51'52, though it is quite difficult to achieve anaerobiosis so complete as to prevent uptake ofnmoles of oxygen. Mononuclear phagocytes from patients with chronic granulomatous disease have a reduced capacity for A D C C in some experimental settingssl but not in others 52,53. Certain macrophage-like cell lines, deficient in production ofO2-, can effectively mediate A D C C 5+. Such observations must be interpreted with some caution, since deficiencies in H202 production may not be complete - particularly in regard to Fc-mediated secretion at the surface of the macrophages. Recent studies have attempted to reconcile these differences by postulating different mechanisms of lysis for different targets 55. Thus, other lytic mediators may well be operative in ADCC, but they remain to be identified. Cytolytic protease does not appear to be a mediator of A D C C 3. Coda Mononuclear phagocytes secrete a wide variety of substances capable of lysing other cells. The destruction of

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tumor cells by macrophages is seen in at least two distinct circumstances: the rapid lysis of targets coated with antibody and the slower lysis of targets not coated with antibody. Although the bases of target recognition and destruction appear to be dissimilar in A D C C and M T C , the cytolytic event in both may be divisible into two stages (i.e. target attachment and target injury). M a n y studies are currently focused on examining the hypothesis that secretory products of'activated macrophages mediate target injury. The present evidence indicates that cytolytic protease and H202 are both important in the destruction of tumor cells by macrophages, but evidence implicating other mediators will doubtless emerge. Ultimately, the importance of the various mediators will probably vary from target to target. A very exciting possibility is that two or more injurious substances can cooperate with one another to effect lysis. As the molecular mechanisms which macrophages, employ for killing tumor cells emerge, it will be important to extend these concepts to studying the destruction of intracellular and extracellular microbial invaders as.well.

Acknowledgements T h e authors' research described here was supported by U S P H S G r a n t s CA-14236, CA-16784, CA-29589 a n d CA-22090. Carl F. N a t h a n is a Scholar of the L e u k e m i a Society o f ' A m e r i c a a n d is in receipt of a n a w a r d from the I r m a T. Hirschl Trust.

References 1 Adams, D. O. and Marino, P. in Contempormy Hematology-Ontology (Gordon, A. S., Silber, R. and LoBue, J., eds), Vol. III, Plenum Publishing, New York (in press) 2 Nathan, C. F. in Macrophage-Mediated Antibody Dependent Cellular Cytotoxicity (Koren, H. S., ed.), Plenum Press, New York (in press) 3 Adams, D. O., Cohen, M. and Koren, H. S. in Macrophage-Mediated Antibody Dependent Cellular Cytotoxicity (Koren, H. S., ed.), Plenum Press, New York (in press) 4 Adams, D. O.,Johnson, W. and Marino, P. A. (1982) Fed. Proc. Fed Am. Soc. Exp. Biol. 41, 2212 5 Nathan, C. F. (1982) Fed. Proc. Fed. Am. Soc. Exp. Biol. 41, 2206 6 Van Furth, R., ed. (1981) Mononuclear Phagocytes Functional Aspects, Martinus-Nijhoff, The Hague 7 Nathan, C. and Cohn, Z. A. (1980)J. Exp. Med. 152, 198 8 Adams, D. O. (1980)J. Immunol. 124, 286 9 Shore, S. L. and Romano, T. J. (1980) Inject. immun. 28, 137 10 Berke, G. and Clark, W. R. (1982) in Mechanisms of Cell Mediated Cytotoxicity (Golstein, P. and Clark, W. R., eds), Plenum Publishing, New York, Adv. Exp. Med. BioL, Vol. 146 11 Nathan, C. F. and Cohn, Z. A. (1980) in Textbook of Rheumatology (Kelley, W. N. and Harrise, E. D., eds), p. 136, W. B. Saunders, Philadelphia 12 Adams, D. O., Kao, K.-J., Farb, R. and Pizzo, S. V. (1980)J. lmmunol. 124, 293 13 Johnson, W. J., Weiel, J. E. and Adams, D. O. (1982) in Natural CellMediated Immunity (Herberman, R., ed.), pp. 949 954, Academic Press, New York 14 Currie, G. A. and Basham, C. (1975)J. Exp. Med. 142, 1600 15 Sharma, S. D., Piessens, W. F. and Middlebrook, G. (198/)) (+'ell. ImmunoL 49, 379 16 Reidarson, T., Levy, W., Klostergaard, J. and Granger, G. A. (1982) J. Natl Cancer Inst. 69, 879 17 Reidarson, T., Granger, G. A. and Klostergaard, J. (1982)ff Notl Cancer Inst. 69, 889 18 DeStefano, J., Beck, G., Lane, B. and Zucker, S. (1982) Cancer Rex. 42, 2O7 19 Chapman, H. A., Vavrin, Z. and Hibbs, J. B. (1982) Cell 28, 653 2O Zucker-Franklin, D., Lauie, G. and Franklin, E. C. (1981)J Hi~tochen7 Cytochern. 29, 451 21 Johnson, W., Pizzo, S. V., Imber, M. and Adams, D. O. (1982) Science 218, 574 22 Johnson, w . J . , Whisnant, C. and Adams, l). O. (1981).]. Immunol 127, 1787

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Mechanisms of autoimmunity: a role for cross-reactive idiotypes Anne Cooke, P. M. Lydyard and I. M. Roitt Ehrlich was rarely given to trivial pronouncements and his recognition of the central importance of the distinction between self and non-self by the immune system, embodied in his concept of 'horror autotoxicus'l, is no exception. This is despite the apparent paradox of the idiotype network in which antibodies recognize self-epitopes on other antibody molecules or antigen receptors as part of the normal process of immune regulation 2. In this review Anne Cooke and her colleagues examine the possible factors which may contribute to the breakdown of self-tolerance and the establishment of autoimmune states. In essence, the diseases associated with autoimmunity in the human may be considered as a spectrum with organspecific disorders such as Hashimoto's thyroiditis and pernicious anaemia at one pole, and non-organ-specific diseases like systemic lupus erythematosus (SLE) at the other. There is a tendency for more than one autoimmune disease to occur in the same individual, although these overlaps are generally restricted to disorders in the same part of the spectrum. Thus, patients with Hashimoto's disease have an unexpectedly high incidence of gastric autoimmunity, but not of SLE. Reciprocally, patients with pernicious anaemia carry a far greater risk of developing thyroid autoimmune disease than do normals, It should be stressed that these associations do not result from paratopic cross-reactions at the B-cell level, as ascertained by the organ-specific reactivity of the patients' sera. This does not, however, exclude the possibility of T-cell cross-reactivity directed against a different epitope, which might also account for the

Department of Immunology, Middlesex Hospital Medical School, London W1P 9PG, UK.

surprising frequency of leucocyte reactivity with mitochondria ~. There does appear to be a genetic basis for this tendency to develop autoimmunity, as evidenced by HI.& associations and family studies which are indicative not just of a predisposition of the immunological system to produce autoantibodies, but also of a preference for a particular organ. For example, although close relatives of Hashimoto and pernicious anaemia patients both have a high incidence of thyroid autoantibodies, the latter also display a much higher frequency of gastric autoantibodies 4. The Obese strain of chicken which spontaneously develops autoimmune thyroiditis provides a similar picture: gastric (proventricular) antibodies are observed with undue frequency 5, and genetic analyses by several workers have identified abnormalities of both the immunological andthyroid-glandsystems 6'7. The workof Cohen and colleagues 7 also implies that the organ itself may be a factor in the development of autoimmune disease. They studied the induction of allergic thyroiditis by immunization with thyroglobulin in Freund's complete adjuvant and showed that when thyroids from genetically high- and low-responder strains were grafted ©1983, El~vicrSciencePublldae~B.V.iAn~erdam 0167E 4919/83/$01.00