Immunoregulatory circuits which modulate responsiveness to suppressor cell signals: contrasuppressor cells can convert an in vivo tolerogenic signal into an immunogenic one

Special regulatory T-cell review: Regulation of immune responses--examining the role of T cells

The history of regulatory T cells goes back to the realisation that T cells could provide 'help' for antibody responses: the obverse of this is their ability to hold them in check. This brief personal overview follows the initial designation of T cells as 'suppressor' and the various hypotheses, some now disproved, put forward for their mechanism of action. We now cautiously label them T regulatory cells, but realise they do not control not all immune regulation. They probably operate through several mechanisms, and some of these are discussed.

A historical perspective on immunological privilege

Intimations of immunological privilege in sites of the body such as the eye and the brain go back in the literature more than a century, to reports of experiments using outbred animals and tumor transplants. The starting points of this review, however, are publications stemming from the transplantation of normal tissues and, as far as possible, the use of inbred animals, exploring the way in which interplay between genetic differences of different degree, from single minor histocompatibility antigens to full-house major histocompatibility complex mismatches, has been reported to affect the 'take' of grafts in putatively privileged sites. While these sites traditionally included the brain, the eye, the pregnancy, and the endocrine tissues such as thyroid, parathyroid, adrenal, and islets of Langerhans, from readings of the literature, it is clear that the eye and the pregnancy have claims to being in the strongest positions of privilege. Even then, the position is precarious, with stirrings of the adaptive immune system poised to attack. Various regulatory mechanisms have now moved center stage and will undoubtedly form a significant part in subsequent chapters in this volume. Perhaps surprisingly, as investigations on these mechanisms have advanced, there is evidence for the convergence of those mechanisms controlling both induced tolerance and immunological privilege.

Immunoengineering: a credible mechanism for CAMPATH-1H action in bone marrow and organ transplantation and the implications for treatment of the immune dysfunction AIDS

Immunoengineering is a term coined to represent the mostly future ability to use or target the immune system's natural components, with emphasis on the regulatory components, to up or down regulate the immune system's attack against specific proteins associated with an unwanted pathology or immune occurrence. It will constitute manipulating parts of the immune system, mostly those specific for the disease associated antigen(s) and generally of a regulatory nature, in various immunological locale or the whole body compartment, to achieve a disease free state for the patient. The number of practical applications awaiting the mastery of immune components as regulatory therapeutics is enormous and immunoengineering should provide treatments in a wide range of disease categories. HIV is a disease where this discipline could provide a quick cure, even eradication of the virus. A potential cheap solution to HIV infection, based on using immunoengineering and adaptable to the infrastructure problems of the Third World is highlighted in the following because of the health emergency that exists in the Third World.

Macrophage T cell interaction. Induction in vitro of a mediator with potent antisuppressor activity

A simple in vitro method is described for the induction of a potent mediator that interferes with suppressor cell function. The mediator consists of three easily identifiable components, Ig, class II determinants and antigen, that form a unique complex similar to, or identical with, the complexes detected in vivo within 3-6 h after immunization. The formation of the antisuppressor mediator in vitro takes place in two steps: the first involves a macrophage-T cell interaction which generates an 'intermediate complex' containing antigen and class II determinants. In the second step the addition of immunochemically purified IgG from normal mouse serum to the macrophage-T cell supernate generates potent antisuppressor activity, which is assayed by the conversion of suppression to immunity. It is suggested that the IgG interacts with the 'intermediate complex' giving rise to the final complex identical to that found in vivo 6 h after immunization. No activity is detected when IgG is added to a supernate of antigen-fed macrophages in the absence of T cells. Furthermore, the T cell plays an additional important role in the formation of the final complexes since it restricts the source of the IgG that will generate the antisuppressor activity. In other words the antisuppressor function is detected only if the IgG matches the donor of the T cell in the Igh locus. The T cell involved in the formation of the complex is the Ly1+ subpopulation. This method should allow elucidation of the genetic, cellular and molecular mechanisms in the activation of this important T cell pathway.

Contrasuppression and tumor rejection

The growth of a highly progressive MCA-induced tumor 3152-PRO is dependent on the activity of suppressor T cells (Ts). Injection of syngeneic mice with antibodies specific for Ts leads to enhanced tumor transplantation resistance of the 3152-PRO tumor. In addition, injection of recipient mice with highly immunogenic regressor tumors conjugated with trinitrophenyl (TNP) activates a T cell population which also mediates protection to transplantation of TNP-conjugated 3152-PRO tumor cells. One such tumor, 1591-RE, was investigated in detail to determine the phenotype and biologic activity of this T cell population in overcoming Ts cell activity. Induction of transplantation resistance requires the presence of TNP hapten on both the highly regressive immunizing tumor (and not its progressor variant 1591-PRO4), and on the challenge tumor 3152-PRO. The cell population from TNP-1591-RE immunized animals which mediates protection against the transplantation of TNP-3152-PRO is Thy-1+, CD4+, 8-, Lyt1+, I-J+, and Vicia villosa lectin adherent, the identical phenotype to antigen-specific contrasuppressor T cells in the contact sensitivity (CS) response to TNP in vivo. A T cell population of identical phenotype from TNP-1591-RE immunized mice can overcome the effects of antigen-specific Ts cells on PCl-immune cells in the adoptive transfer of CS in vivo. These results suggest that immunoregulatory cells that mediate protection against progressive tumors may be identical in function to antigen-specific contrasuppressor T cells.

Contrasuppression in autoimmunity. Abnormal contrasuppression facilitates expression of nephritogenic effector T cells and interstitial nephritis in kdkd mice

We have used the murine model of spontaneous autoimmune interstitial nephritis in kdkd mice to examine the importance of abnormal immunoregulation in the expression of disease. T cells from naive congenic CBA/Ca mice suppress both histologic renal injury in the kdkd strain as well as the DTH reactivity to CBA/Ca renal tubular antigens mediated by lymphocytes from nephritic kdkd mice. These antigen-specific suppressor T cells are Lyt-2+, L3T4+, I-Jk+, genetically dominant and I-Jk restricted. Unfractionated spleen cells from young, prenephritic kdkd mice also demonstrate such suppressor function. Shortly preceding disease onset, however, net suppression is functionally bypassed by emergent contrasuppressor T cells. These regulatory cells are also Lyt-2+ and I-Jk+, and adhere both to the Vicia Villosa lectin and CBA/Ca TBM. By admixing these contrasuppressor cells with spleen cells from non-disease-prone CBA/Ca mice we were able to demonstrate the presence of DTH-reactive and nephritogenic effector cells in the latter population. Such nephritogenic effector cells could also be simply demonstrated after depletion of the suppressor cells with anti-I-Jk mAbs and complement. These findings support a role for contrasuppressor cells in the abrogation of tolerance to parenchymal self-antigens.

Isotype-specific immunoregulation. Evidence for a distinct subset of T contrasuppressor cells for IgA responses in murine Peyer's patches

The ability of murine Peyer's patch (PP) T contrasuppressor cells (Tcs) to reverse oral tolerance to the T cell-dependent (TD) antigen SRBC was studied both in vivo and in vitro. C3H/HeJ mice given SRBC orally for 4 wk are not rendered tolerant to this antigen and were used as a source of PP Tcs cells for adoptive transfer to identically treated, orally tolerized C3H/HeN mice. Transfer of 10(4) or 5 X 10(4) V. villosa-adherent PP T cells resulted in splenic IgM, IgG, and mainly IgA responses in C3H/HeN mice challenged systemically with SRBC. The T cell responsible was Lyt-1+, 2-, L3T4-, I-JK+ and V. villosa lectin-adherent, all characteristics of mature effector Tcs cells. This C3H/HeJ PP Tcs cell subset was also effective when added to in vitro cultures of tolerized spleen cells derived from SRBC-fed, C3H/HeN mice. Interestingly, C3H/HeJ PP Tcs cells restored mainly IgA responses when transferred in vivo or when added to suppressed C3H/HeN splenic cultures. Comparison of the functional activity of Tcs cells derived from spleen or PP of orally immunized C3H/HeJ mice revealed that splenic Tcs cells supported responses of all 3 isotypes; however, PP Tcs cells yielded three-fourfold higher IgA responses, when compared with IgM or IgG anti-SRBC responses. Adherence of C3H/HeJ PP Tcs to an Fc alpha R+ T cell line derived from IgA-specific Th cells resulted in a nonadherent cell fraction that potentiated only IgM and IgG responses, while bound Tcs cells preferentially supported IgA responses. These results suggest that murine PP contain IgA-specific Tcs cells that allow IgA response induction in the presence of Ts cells that mediate oral tolerance.

Increased amplifier T cell activity in autoimmune NZB mice and its possible significance in the expression of autoimmune disease

The expression of amplifier- and helper-T cell activity was examined in NZB/N mice of different ages. Amplifier T cell activity develops in a cyclic manner; it decreases between 16 and 35 wk of age and then increases to maximal levels in mice older than 50 wk of age. The loss of suppressor T cell activity and increased amplifier T cell activity coincide with the development of autoimmune diseases in aging NZB/N mice. Although helper T cell activity is evident in young NZB/N mice, it is absent in old NZB/N mice expressing maximal amplifier T cell activity. This provides additional support for the fact that amplifier and helper functions are mediated by different subpopulations of T cells.

Oscillation of antibody production and regulatory T cells in response to antigenic stimulation

Priming with the T-dependent antigen trinitrophenylated horse red blood cells led to an oscillatory response of plaque-forming cells (PFC) with peaks of response after 4, 8, 12 and 16 days. Limiting dilution (LD) analysis of regulatory T cells indicated that the response is partly due to activation of helper T cells (Th), but mainly is the result of release from suppression by activation of a third regulatory T cell (T3) population (Zöller, H. and Andrighetto, G., Immunology 1985. 55: 703). Priming resulted in consecutive activation of suppressor T cells (Ts; day 1-3), a population regulating Ts (T3; day 2-4) and of Th (day 4). Furthermore, regulatory elements displayed a cyclical behavior like PFC. Th and T3 oscillated within a period of 4 days in phase with PFC, while Ts oscillated phase-shifted to PFC, Th and T3. Hence, oscillation of PFC after priming with a T-dependent antigen is the result of interactions among regulatory T cells. The data are interpreted as follows. Th are the primum movens of the oscillatory behavior of PFC response, since Th oscillate in phase with PFC and display the same pattern of decreasing amplitudes as PFC. However, the basic regulatory elements are Ts and T3 which are interlinked and oscillate phase shifted. As revealed by the time-course analysis of LD curves, T3 function as suppressor cells for Ts. Hence the status of mutual interactions of Ts and T3 determines suppression of Th or release from suppression, i.e. when T3 are found at high frequencies, Th are released from suppression, since T3 suppresses Ts. Instead, the increase in the frequency of Ts and their predation on Th determine the decrease of the frequency of Th. Thus, these data support the hypothesis of a circular network, the central regulatory core being composed of two elements, Ts and T3, with mutual suppressive activity.

Antigen presentation by spleen dendritic cells

It is now recognized that dendritic cells (DC) isolated from mouse spleen play an important role in activating T lymphocytes. These DC, which show many similarities to veiled cells found in the paracortical regions of spleen and lymph node, may be closely related to the epidermal Langerhans cells. It is known that DC are extremely effective allostimulators. We have also found that although DC lack demonstrable phagocytic ability, they are extremely potent at presenting soluble polypeptide antigens to primed T cells. Since T lymphocytes comprise several distinct subsets (particularly cytotoxic, helper, and suppressor) in our most recent studies we have asked whether DC are able to trigger all these different subsets of T cells. We examined the ability of different spleen cell types coupled with the hapten NP to induce antigen-specific T suppressors for a delayed type hypersensitivity (DTH) response. It was found that T suppressors were generated only when hapten was conjugated to a spleen-derived antigen-presenting cell. Further analysis revealed that macrophages but not DC were able to induce defined sets of suppressor cells in vivo (although DC were able to trigger a very powerful DTH response). We also examined the ability of DC to activate T cells which are required to cooperate with B cells in the production of antibody. Even though DC were able to trigger T lymphocytes to produce lymphokines, these activated T cells did not act as helper cells in a standard hapten-carrier system. Possible mechanisms for this dichotomy of DC function are discussed.

Selection of the delayed hypersensitivity T effector and T suppressor cell response by antigen-presenting macrophages

The T effector lymphocytes of delayed type hypersensitivity reactions (TDH) are regulated by a complex T suppressor (Ts) cell circuit. Induction of TDH cells requires Ia+ adherent cells as antigen-presenting cells. Little is known about the antigen presentation of the induction of Ts cells. We describe an experimental model in which TDH and Ts cells are induced separately by different antigen-presenting macrophages grown from bone marrow stem cells. Bone marrow derived macrophages grown in L cell-conditioned medium for various periods and labeled with 2,4-dinitrobenzene sulfonic acid differ in their ability to induce TDH and Ts cells in vitro. The functional activity of the two T subpopulations was assessed in vivo by epicutaneous challenge or sensitization with 2,4-dinitrofluorobenzene of mice receiving the in vitro educated cells. Ear swelling or suppression of swelling was recorded. It could be shown that 5-7 day bone marrow-derived DNP-labeled macrophages preferentially induced Thy 1+ Lyt 1+ antigen-specific TDH cells; 7-10 day old antigen-presenting bone marrow-derived macrophages induced preferentially Thy 1+ Lyt 2+ antigen specific Ts cells. Characterization of various phenotypic markers revealed different surface antigen expression and functional differences such as MIF responsiveness or transglutaminase activity on the two macrophage populations. These data support the concept that activation of the Ts regulatory circuit may require antigen presentation by specialized antigen presenting cells, characterized by certain surface and functional markers and different from those inducing preferentially TDH cells.

Regulation of the antibody response to type III pneumococcal polysaccharide by contrasuppressor T cells

A soluble membrane component of type III pneumococcal polysaccharide-coupled spleen cells (S3-SCSM) induces S3-specific suppressor T cells (Ts) in mice. These Ts can be detected only if mice are pretreated with cyclophosphamide (Cy) or if cells adherent to the lectin Vicia villosa are removed from the spleen cell population prior to transfer. The V. villosa-adherent spleen cells from mice injected with S3-SCSM could abrogate suppression mediated by Ts induced by S3-SCSM in Cy-treated mice. The V. villosa-adherent contrasuppressor cells were shown to be T cells that were I-J+ and of the Lyt-1 phenotype. Contrasuppressor T cells (Tcs) were not present in V. villosa-adherent spleen cell fractions obtained from normal mice, from mice injected with polyvinylpyrrolidone-coupled spleen cells, or from Cy-treated mice injected with S3-SCSM, i.e., mice in which Ts activity is dominant. The V. villosa-adherent cells that abrogated the activity of Ts induced by S3-SCSM in Cy-treated mice did not abrogate suppression mediated by a different subset of S3-specific Ts, suggesting that the Tcs described here do not have activity against all Ts subsets. The ability of S3-SCSM to activate Tcs in normal mice provides an explanation for the inability to detect S3-specific Ts in several previous studies.

Differential induction of help and suppression in mice by bifunctional antigens administered via different routes

Bifunctional antigens composed of one L-tyrosine-p-azobenzenearsonate (Tyr-ABA) carrier epitope and one dinitrophenyl (DNP) haptenic epitope separated by 6-aminocaproyl or polyprolyl spacers induced weak IgM anti-DNP plaque-forming cell (PFC) responses in the spleens of mice immunized intraperitoneally, without detectable IgG PFC. However, the same antigens introduced into the footpads induced IgG PFC responses in the draining lymph nodes which rose to levels greater than 100/10(6) viable lymphocytes. Moreover, the response in the lymph nodes to booster injections of antigen was characteristic of secondary T-dependent antibody responses, whereas the splenic secondary response simply mirrored the primary. The magnitude of the IgG PFC response was influenced by the size of the spacer and by the strain of mice, although genetic control did not map to the major histocompatibility complex. Prior i.p. immunization suppressed the IgG response to subsequent immunization in the footpads. This suppression could be transferred to normal syngeneic recipient mice with spleen cells from suppressed donors. Suppressor activity was eliminated by treating the spleen cells with anti-Thy-1 antibody prior to transfer, establishing the T-cell dependency of suppression. Suppression was also induced by Tyr-ABA itself, but not by DNP-lysine, indicating the epitope specificity of the suppressor cells. Thus, bifunctional antigens induce dominant suppression in the spleen but significant help in lymph nodes.

Contrasuppression: the second law of thymodynamics, revisited

The data discussed here touch upon several issues in the evolving story of T cell contrasuppression, the underlying theme being that of heterogeneity. First, there is the issue of function. We are considering here only those cells that affect the function of secretory differentiation. We have evidence that different contrasuppressor cells exist for clone growth, but have not yet studied them in the same depth as those for secretory differentiation. Second, there is the important issue of target cells. In this article by Green and Gershon it is pointed out that there is clear evidence that contrasuppressor effects can work by protecting helper cells from suppressor cell effects in vitro. On the other hand, direct additional inhibition of the suppressor cells themselves has not been excluded. The latter point is also true in our system. However, we must suppose for the sake of simplicity in many of our experiments that if suppressors are not the target of the contrasuppressor effects then the B cells themselves probably are. This is because the tumor cells engage in a spontaneous rate of growth and differentiation in the absence of help or suppression. When T cell-dependent, specifically triggered effects reduce this spontaneous behavior, then a suppressive effect must have been delivered directly to the B cells. This is a simplifying assumption which is attractive, but since the experiments are carried out in vivo and thus may be affected by some factors that we have not yet recognized, we are not confident on its "intuitive" appeal. A third issue revolves around triggering specificity. One of our contrasuppressors exhibits the phenomenon of carrier crossreactivity (CRCS) and is thus behaving in accord with expectations aroused by Green and Gershon in this review. The other cell is apparently quite carrier specific (SCS). The meaning of this is not at all clear, but its potential significance may somehow be related to a sort of "mirror image" relationship of the two cells. Thus, for example, in other experiments not discussed here, we have noted that the CRCS binds to 315 protein-coated plates, but as noted here counteracts a suppressive effect which is generated by cells which do not adhere to these plates. In contrast to SCS does not bind to 315 plates and yet, as noted here, appears to counteract a suppressor effect generated by cells which do adhere to 315 plates.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of contrasuppression in the adoptive transfer of immunity

The data presented in this paper show that the population of cells that adoptively transfer contact hypersensitivity are Lyt-1+ 2-, I-J- and nonadherent to V. villosa lectin. However, the adoptive transfer of immunity by this population of cells is successful only when the recipient has been treated in such a way as to impair the host immunosuppression mechanism. This population cannot, on its own, transfer immunity to adult, untreated naive recipients unless an additional population of immunoregulatory cells is present. This immunoregulatory population does not itself adoptively transfer immunity. This latter population is differentiated from the immune cells in that they are Lyt-1+ 2-, I-J+ and are adherent to V. villosa lectin. Both populations are required to adoptively transfer immunity to adult untreated naive recipients.

Aging and the immune system

Information is presented on changes in the aging immune system. An analysis of separate streams of cellular aging in the inbred mouse is presented. It is demonstrated that there is extensive polymorphism in the aging of different types of executive and regulatory cell lines.

Immunoregulatory circuits which modulate responsiveness to suppressor cell signals: characterization of an effector cell in the contrasuppressor circuit

Spleen cells from neonatal animals, placed in culture for 6 days spontaneously develop the ability to block the activity of suppressor T cells, a phenomenon that is referred to as contrasuppression. The effector cell which is derived from the interactions among the cells which comprise a contrasuppressor "circuit" is an Ly-1 T cell. It can be separated from Ly-1 helper cells by three criteria other than function: its generation is dependent on Ly-2+ cells, it is I-J+, and it sticks to the Vicia villosa lectin. Those cells which deliver help to B cells under the experimental conditions studied are not dependent on Ly-2+ cells for generation and neither express determinants that our anti-I-J antisera recognize nor stick to V. villosa. The mechanism by which these Ly-1 contrasuppressor cells function was elucidated by adding them to "'intermediate cultures" containing activated Ly-2 suppressor cells and in vivo immunized Ly-1.1-congenic helper cells. After 48 h in these intermediate cultures, the neonatal Ly-1.2 contrasuppressor cells and the Ly-2 suppressor cells were removed by treatment with the appropriate antiserum plus complement. The remaining activity of the in vivo generated Ly-1.1 helper cells was assayed in fresh cultures of B cells. The contrasuppressor cells not only diminished suppression of the Ly-1 helper cells by the Ly-2 suppressor cells in the intermediate culture, but actually conferred a state of relative resistance to suppression upon the helper cells. This state persisted after the contrasuppressor cells were removed. Why such a cellular circuit, which confers resistance to suppression, might be beneficial to neonatal mice and how considering its attributes might help explain some immunological paradoxes is the subject of discussion.