The fundamental T cell proliferative repertoire in a nonresponder strain and its qualitative alteration by suppression

B10 mice, although genetically nonresponsive to hen egg-white lysozyme (HEL) after i.p. immunization due to suppressor T cells, make a vigorous helper and proliferative T cell response in the draining popliteal lymph nodes (P-LN) soon after footpad immunization with HEL. The fundamental specificity repertoire in B10 P-LN analyzed with cross-reactive lysozymes, was then compared with that found after the delayed appearance of suppression, in the PETLES. In contrast with B10.A mice, whose T cell specificity pattern was unchanged with time, or anatomical site, the onset of HEL-induced suppression in B10 mice led to a marked heteroreactive shift in specificity pattern. This shift did not occur after immunization with REL (ring-necked pheasant lysozyme), which fails to induce suppression.     

Delayed-type hypersensitivity to hen egg-white lysozyme. I. The surface phenotypes of suppressor T cells induced by intravenous injection of lysozyme-modified spleen cells, and their molecular interactions

Suppressor T cells (Ts) induced by lysozyme-modified syngeneic lymphocytes were characterized. Hen egg-white lysozyme (HEL)-specific delayed-type hypersensitivity (DTH) was suppressed when HEL-induced Ts were transferred into naive mice. These HEL-induced Ts had surface markers of both Thy-1 antigen, and I-J gene products. The suppression of HEL-specific DTH was greatly increased, when these Ts had been enriched with HEL-coated petri dishes. Isolated anti-HEL antibodies from B10.BR or A/Sn mice were inoculated into rabbits to induce anti-cross-reactive idiotype (CRI) antibodies. The rabbit antisera were extensively absorbed with normal B10.BR or A/Sn immunoglobulins (Igs) and MOPC 104E ascites Igs to render them idiotype (Id) specific. Using these anti-CRI antibodies, we observed that these Ts possessed Id receptors on their cell surface. Results of both fluorescence techniques and cytotoxicity tests revealed that about 10% of the enriched T cells containing these Ts were Id positive. Moreover, these enriched T cells were substantially killed by anti-I-J antiserum plus complement. However, this killing was completely blocked by HEL antigen. These results suggest that both Id receptors and I-J gene products might be forming the same molecular complexes or might coexist in the vicinity of the molecule.     

Amino acid residues distinct from the determinant region can profoundly affect activation of T cell clones by related antigens

Hen egg-white lysozyme (HEL)-specific T cell clones derived from the C57BL/6 strain were found to be about 100-fold more sensitive to the closely related ring-necked pheasant lysozyme (REL) in a dose-dependent proliferation assay. This apparent heteroclicity of REL was independent of the fine specificity of the clones. However, when stimulations by corresponding cyanogen bromide-cleaved peptides (L2H and L2R) known to contain the determinants recognized by all of the clones were compared, the preference for REL was lost. Conversely, an HEL-specific, I-Ad-restricted clone that did not respond to REL responded equally well to L2H and to L2R. Because the HEL/REL reactivity differences involved only the T cells and antigen-presenting cells (APC), and were correlated with differential sensitivity to the lysosomotropic drug chloroquine, it appears that the reactivity differences relate to the manner in which lysozymes are processed by the APC. Thus, conclusions about T cell "clonal specificity," usually attributed to differences in recognition of the determinant regions, may in some cases reflect differential antigen handling that depends on sites on the molecule distant from the determinant.     

Suppression of the delayed-type hypersensitivity response to hen egg white lysozyme (HEL) by HEL peptides in a genetically high-responder mouse strain: evidence for requirement of the loop structure for induction of suppressor T cells

The delayed-type hypersensitivity (DTH) response of C3H/HeN mice to hen egg white lysozyme (HEL) can be blocked by a single iv injection of a solution of HEL in buffered saline 7 days before sensitization of animals with HEL in complete Freund's adjuvant (CFA). The minimal structure of HEL required for the suppression was examined by determining the abilities of various HEL-derivative peptides to inhibit HEL-DTH. Treatment of normal mice with Ploop I X II, sequence 57-107 (Cys64-Cys80, Cys76-Cys94), or P17 (sequences 1-27 and 123-129 linked by Cys6-Cys127) 7 days before immunization with HEL resulted in marked suppression of the DTH response. This inhibition of DTH involved generation of suppressor T cells (Ts). The results suggested that two suppressor pathways are involved. These data, together with another recent finding (1) that an entirely different portion of HEL is a suppressor determinant (SD) in A/J mice, indicate that different epitopes act as SDs in different strains of mice. Of the loop region peptides tested, Plc (intact loop I joined to a linear peptide, residues 84-97) was found to be the minimum structure capable of suppressing the HEL-DTH response; loop I or II alone did not cause suppression. Activation of Ts cells by the loop peptide depended on its conformational structure; completely reduced and carboxymethylated Ploop I X II did not cause suppression.     

Regulatory mechanism of delayed-type hypersensitivity in mice. IV. Effect of suppressor T cells on the development of memory T cells involved in accelerated generation of DTH-effector cells in vitro

The effect of suppressor T cells (Ts) on the induction and the subsequent development of memory T cells for delayed-type hypersensitivity (DTH) was examined. The memory cells were induced in the spleens of mice primed previously with a low dose of reduced and alkylated ovalbumin (Ra-OA), and they generated DTH-effector T cells (DTH-Te) in a significantly accelerated fashion when cultured with OA in vitro. Ts were obtained from the spleens of mice which received OA-coupled spleen cells i.v. 4 days previously, and they inhibited antigen-specifically the induction of DTH responses in the recipient mice sensitized with alum-absorbed OA only when transferred with 5 weeks before sensitization. The spleen cells from mice given Ts together with the priming antigen 7 weeks before culture failed to generate DTH-Te in an accelerated manner on restimulation with OA in vitro. The memory cells from primed mice also did not cause accelerated generation of DTH-Te, when cultured with Ts in the presence of OA in vitro. These results indicate that both the induction of the memory cells by priming with antigen in vivo and the subsequent development of memory cells to DTH-Te by restimulation in vitro are inhibited independently by Ts. This corresponded well with the effect of Ts on the development of DTH-memory in vivo.     

Suppression of Hen Egg-White Lysozyme (HEL)-Specific Delayed-Type Hypersensitivity Responses in Mice by Suppressor T Cells after Neonatal Administration of Anti-Idiotypic Antibodies

Anti-idiotypic rabbit antiserum (anti-Id) directed to the idiotypes of anti-hen egg-white lysozyme (HEL) antibody from a single C3H mouse (No. 2) was shown to be capable of recognizing only a fraction of the anti-HEL antibody populations produced by other C3H mice. Experiments were performed to examine the effect of this particular anti-Id on the delayed-type hypersensitivity (DTH) response specific for the same protein antigen. A group of 60-day-old C3H mice which had been administered anti-Id within 24 hr after birth were tested for HEL-DTH response. The results indicated that the DTH response was completely suppressed by the anti-Id treatment. The inhibition of DTH reactivity is due to active suppression and involves the generation of suppressor T cells. Thus, the suppression induced with a single injection of anti-Id was transferable with both spleen cells and thymocytes from mice that received anti-Id. These suppressor cells are T cells since their ability to suppress DTH is completely abrogated by treatment in vitro with anti-Thy 1.2 serum and complement.     

Hapten-specific responses to the phenyltrimethylamino hapten. IV. Occurrence of mechanistically distinct idiotypic suppressor T cells before the appearance of anti-idiotypic suppressor T cells induced by the monovalent antigen L-tyrosine-p-azophenyltrimethylammonium

We have previously shown that a single i.p. injection of the monovalent synthetic antigen, L-tyrosine-p-azophenyltrimethylammonium [tyr(TMA)] in complete Freund's adjuvant induces an anti-idiotypic T suppressor cell (Ts2) population that can be detected 6 wk later by its ability to shut down delayed-type hypersensitivity (DTH) specific for the TMA hapten. In this paper we present evidence that 2 wk after tyr(TMA) administration, a subset of Ts, termed Ts1, appears that is both functionally and phenotypically distinct from the late appearing Ts2 population. The early occurring Ts1 act only at the induction phase of the DTH response and can also suppress this response intrinsically. This latter point is in marked contrast to our previous observation that the tyr(TMA)-induced anti-idiotypic Ts2 fail to function intrinsically and can only be detected upon adoptive transfer into naive mice. Ts1 bear idiotypic receptors and are Ly-1+,2- in contrast to the anti-idiotypic Ly-1-,2+ Ts2 population. In addition, unlike the Ts2 population, Ts1 are comparatively nylon wool-adherent. Adsorption of Ts1 on either antigen- or idiotype-coated petri dishes indicate that the suppressor activity can be transferred only by antigen-binding cells. Cellfree factors prepared from spleens containing the Ts1 population can suppress DTH only if administered at the induction phase of the response, in contrast to the factors derived from the Ts2 population that act both at induction as well as effector phases, suggesting that Ts1 and Ts2 can function via soluble mediators. Finally, we show that when Ts1-bearing mice are primed and boosted for anti-TMA antibody formation, the resulting response was overall reduced with respect to the idiotype-positive and negative plaque-forming cells that differs from the Ts2-bearing hosts wherein the idiotypic component is preferentially suppressed. The appearance of Ts1 before the detection of Ts2 in the same experimental animals is discussed with reference to a normal physiologic sequence of events involved in suppressor pathways.     

Functional analysis of cloned macrophage hybridomas. VI. Differential ability to induce immunity or suppression

We previously screened a series of macrophage hybridomas derived from fusion of P388D1 (H-2d) tumor cells with CKB (H-2k) splenic adherent cells for their ability to induce I-J restricted Ts cell responses. One Ia+ macrophage clone (63) consistently induced Ag-specific, I-J-restricted Ts. To evaluate whether macrophage hybridoma 63 also induced delayed-type hypersensitivity (DTH) immunity, mice were immunized with hapten-coupled macrophage hybridoma cells. Hapten-coupled splenic adherent cells and control macrophage hybridomas induced significant primary DTH responses, whereas hapten-coupled macrophage 63 induced little or no immunity when injected into H-2 compatible hosts. However, macrophage hybridoma 63 specifically activated I-Ak, I-Ad, or I-Ed restricted T cell hybridomas/clones, in vitro in the presence of appropriate Ag. Three different strategies designed to eliminate suppressor cell activity were successfully used to demonstrate that hapten-coupled macrophage 63 could also induce in vivo immunity. First, after immunization with hapten-coupled macrophages, mice were treated with cyclophosphamide. Second, macrophage 63 was treated with anti-IJ idiotype antibody before 4-hydroxy-3-nitrophenyl acetyl hapten (NP) coupling. Finally, haptenated macrophages were injected into I-A compatible but I-J incompatible recipients. These protocols are known to inhibit the induction of Ts activity, thus these results indirectly suggest that there is stimultaneous generation of Ts activity in vivo. The latter hypothesis was tested in adoptive transfer experiments. Transfer of lymph node cells from NP-63 primed B10.BR (H-2k) mice induced immunity in naive 4R animals, whereas the same number of immune cells suppressed NP-induced DTH responses in 5R mice. The combined results indicate that a cloned macrophage line can activate both Th and Ts cells. Macrophages which induce Ts activity may be responsible for maintaining the balance of immunity vs suppression. The data support the hypothesis that IJ interacting molecules (IJ-IM) expressed on macrophages are critical for induction of suppressor cell activity.     

Prevention of granuloma development in the mouse by using T cell hybridoma products

The ability of an azobenzenearsonate (ABA)-specific suppressor T cell factor, a soluble extract from first order suppressor T cells (Ts1), and suppressor molecules produced by a long-term T cell hybridoma to regulate ABA-specific granuloma formation was studied. ABA-derivatized syngeneic spleen cells (ABA-SC) administered subcutaneously induced persistent delayed-type hypersensitivity (DTH) responses, detected by footpad swelling and hapten-specific granuloma formation by 72 and 96 hr after challenge with ABA-bovine serum albumin coupled to polyacrylamide beads (ABA-BSA-PAB). Soluble factors from ABA-specific Ts1 prevented DTH and granulomatous development after subcutaneous administration of ABA-SC. Moreover, the in vivo administration of a factor that is derived from a Ts1 functioning hybrid cell line induced a second set of suppressor cells (Ts2) that upon transfer to syngeneic ABA-primed mice were able to inhibit granuloma formation in the footpad, as well as in the gastrointestinal tract after challenge with ABA-BSA-PAB. These experiments demonstrate the dependence of the granulomatous reaction on T cell-mediated events, as well as the potential therapeutic efficacy of an antigen-specific suppressor T cell factor and a hybridoma T cell product in limiting antigen-specific granuloma formation in vivo.     

In vitro generation of suppressor T cells. Induction of CD3+, IgH-restricted suppressor cells

Previous studies of the immune response of C57BL/6 mice to the 4-hydroxy-3-nitrophenyl acetyl (NP) hapten determined that challenge with antigenic forms of hapten induces both immunity and suppression. The anti-NP plaque-forming cell response can be down regulated by an Ag-induced cascade consisting of three suppressor T cell subsets. These three populations, termed Ts1, Ts2, and Ts3 have been characterized to have inducer, transducer and effector functions, respectively. Although the functions of each of these subsets have been examined in vivo, the cellular requirements for in vitro Ts induction have only been investigated for the Ts3 population. The present study characterizes the cellular events that lead to the induction of the Ts2, suppressor transducer population. Culture of naive C57BL/6 spleen cells with Ts1-derived suppressor factor in the absence of exogenous Ag leads to the generation of Ts2 cells that mediate Ag-specific suppression of NP plaque-forming cell responses. Phenotypic analyses demonstrate that a CD3+, CD4-, CD5+, CD8+, and I-J+ precursor population is stimulated by TsF1 to become mature Ts2 cells that express CD3, CD8, and I-J but not CD5. Although previous studies have reported an essential role for B cells in the induction of other Ts populations, depletion of B cells from Ts2 induction cultures had no effect on Ts2 generation. Despite the absence of B cells in these cultures, the mature Ts2 cells were functionally IgH restricted. Studies with IgH congenic B.C-8 mice suggest that this restriction specificity was imposed by the idiotype-related determinants expressed on the TsF1, not the T cell genotype.     

Differential influence of 2'-deoxyguanosine on the induction and expression of suppressor T lymphocytes in vivo

Subcutaneous (sc) immunization of mice with allogeneic spleen cells can induce delayed-type hypersensitivity (DTH) to histocompatibility antigens. Intravenous immunization with irradiated allogeneic spleen cells, on the other hand, induces suppressor T (Ts) lymphocytes. These Ts cells are capable of suppressing the host-versus-graft (HvG) DTH reactivity which normally arises after sc immunization. Moreover they can suppress the development of antihost DTH effector T cells during graft-versus-host (GvH) reactions. These models for HvG and GvH DTH reactivity were used to study the influence of 2'-deoxyguanosine (dGuo) on the induction, further development, and expression of Ts cells in vivo. It was found that administration of dGuo inhibits the proliferation-dependent induction and further development of Ts cells, but not the suppression mediated by already activated Ts cells.     

A limited region within hen egg-white lysozyme serves as the focus for a diversity of T cell clones

The C57BL/6 (H-2b) mouse is a nonresponder to hen egg-white lysozyme (HEL) injected i.p., owing to a T suppressor cell-inducing determinant at the amino-terminal region. After immunization with a 93-amino acid fragment (a.a. 13-105) of HEL lacking this determinant, all clones from two independently derived C57BL/6 T cell lines were found to be specific for epitopes within a subregion of peptide 74-96. Three specificity patterns for the clones could be defined on the basis of cross-reactivities with only two other species variant lysozymes. Reactivities of all three specificity groups was consistent with the serine to threonine substitution at position 91, although reactivity of one of the groups could be affected by substitutions at position 84. The results confirm at the clonal level that even for distantly related antigens, only limited regions are recognized by T cells. They are consistent with the notion that specific sites on the antigen capable of interaction with Ia molecules lead to dominance of certain regions for T cell reactivity. Moreover, the diversity in specificity among clones suggests that the limiting feature of T cell responsiveness is not a lack of available T cells in the repertoire directed against a single antigenic site.     

B-cell-mediated regulation of delayed-type hypersensitivity

We obtained immune sera from mice which received suppressor B cells induced in vitro, injected them into immunized mice, and measured suppression of the delayed-type hypersensitivity (DTH) of these recipient mice. In the recipients, effector-phase suppressor T (Ts) cells were induced, and the action of these Ts cells was antigen-nonspecific. The suppressive material of the sera was adsorbed on a Sepharose column coated with anti-mouse immunoglobulin antibody and acid elution of the column yielded the elute fraction that showed significant suppressive activity. The suppressive activity of the sera was also adsorbed by an antigen-coated Sepharose column, and the eluate from the column had suppressive activity. Moreover, we established antigen-specific monoclonal antibodies, some of which suppressed the DTH in an H-2-nonrestricted way. The isotype or specificity of the antibodies was not related to the suppression, because suppressive and nonsuppressive antibodies belonged to the same immunoglobulin isotype and because the antibodies that recognized the same epitope had different suppressive activities. The Fc portion was not the functional site, because the F(ab')2 fragment had the activity. The suppressive antibody induced effector-phase Ts cells, which had the anti-idiotypic receptor. These findings suggested that antigen-specific antibodies in the immune sera mediated the suppression of DTH by the induction of effector-phase Ts cells in vivo and the idiotype of the antibody stimulated the anti-idiotypic receptor of these Ts cells.     

Immunologic regulation of experimental cutaneous leishmaniasis. V. Characterization of effector and specific suppressor T cells

Resistant CBA mice infected with Leishmania tropica promastigotes develop concomitant and convalescent immunity against reinfection. This can be adoptively transferred by splenic and lymph node T cells with a threshold dosage of 1 to 2.5 x 10(7). The effector cells are of Thy-1+, Lyt-1+2- phenotype. The same immune cell population also adoptively transfers specific DTH to L. tropica, which is restricted by the major histocompatibility complex. On the other hand, highly susceptible BALB/c mice infected with L. tropica develop antigen-specific suppressor T (Ts) cells (previously shown to inhibit the induction and expression of DTH), which are capable, on transference, of reversing the healing of lesions induced by prior sublethal irradiation of BALB/c mice. As few as 10(6) of these T cells are effective in abrogating the potent prophylactic effect of 550 rad. The Ts cells are of Thy-1+, Lyt-1+2-, and I-J- phenotype. Sublethally irradiated and infected BALB/c mice produce antibody responses quantitatively and isotypically similar during the critical first 40 days after infection whether or not they are injected with 10(7) Ts cells (nonhealing vs healing). Thus, impairment of DTH and curative immune responses in BALB/c mice cannot be attributed to a helper function of these Thy-1+, Lyt-1+2- cells for the formation of suppressive antibody.     

Regulation of cell-mediated immunity in cryptococcosis. II. Characterization of first-order T suppressor cells (Ts1) and induction of second-order suppressor cells

Cryptococcosis patients frequently have high levels of cryptococcal antigen in their body fluids, and the levels of circulating antigen can generally be used to predict the patient's recovery, with high or rising antigen titers indicating a poor prognosis and low or decreasing levels a good prognosis. In a previous study, we reported on a murine model for studying the effects of cryptococcal antigen on host defense mechanisms. In that work, we demonstrated that an i.v. injection of cryptococcal antigen (CneF) into CBA/J mice, to simulate the antigenemia known to occur in human cryptococcosis, induced a population of T suppressor cells (Ts1) in the lymph nodes (LN). Upon adoptive transfer, the Ts1 cells specifically suppressed the afferent limb of the delayed-type hypersensitivity (DTH) response to cryptococcal antigen. In the present study, we show that the precursors of the Ts1 cells are sensitive to low-dose cyclophosphamide treatment and that the phenotype of the Ts1 cells is Lyt-1+, Ia+ (I-J+). LN cells from CneF-injected mice or a soluble factor derived therefrom can induce in the spleens of recipient mice a second-order suppressor cell population that suppresses the efferent limb of the DTH response. The cells that induce the second-order or efferent suppressor cells have the same phenotype as the cells that appear to suppress the afferent limb of the DTH response. The findings in this study indicate that a complex regulatory mechanism is responsible for the observed suppression of the DTH response in this infectious disease model. Furthermore, the suppressive circuit thus far defined for cryptococcal antigen is similar to the antigen-specific suppressor cell pathway outlined for certain chemically defined haptenic systems.     

Requirements for suppressor cell activation. Role of accessory cells

In the 4-hydroxy-3-nitrophenyl acetyl (NP) suppressor system, third order suppressor cells (Ts3) subset of suppressor cells is generated after Ag priming, but, in order to express suppressor activity, these cells need to be further activated or triggered with a specific second order suppressor factor. By in vitro activation of Ts3-containing lymph node cells or a pTs3 hybridoma we now show that macrophages are also required for Ts3 activation. In addition, we demonstrate that IJ genetic restrictions control this activation process. Furthermore, we directly demonstrate Ts3 activation using cloned macrophage hybridoma cells. To further investigate the interactions between Ts3 cells and the accessory cells involved in their activation, we attempted to block the second order suppressor factor mediated activation of Ts3 cells with antibodies. The activation of Ts3 cells can be blocked by the addition of anti-IJ, anti-IJ idiotype or anti-NPb idiotype antibodies, but not by anti-CD8, anti-IA, or anti-IE antibodies. Anti-IJ mAb blocked Ts3 activation at the lymphocyte level whereas anti-IJ idiotype blocked activation at the accessory cell level. Finally we tested, whether these antibodies can also directly activate primed Ts3 cells. We demonstrate that cross-linked anti-IJ, anti-NPb and anti-CD3 antibodies can activate Ts3 cells. The results are discussed in terms of receptor-ligand structures on Ts and accessory cells which are required for the activation of Ts3 cells.     

Selection of similar naive T cell repertoires but induction of distinct T cell responses by native and modified antigen

To study the T cell responses induced by native and modified Ag, we have followed in vivo TCR selection and cytokine profile of T cells, as well as the isotype of induced Abs, in response to the model Ag hen egg-white lysozyme (HEL) and its reduced and carboxymethylated form (RCM-HEL). RCM-HEL induces in vivo a T cell response focused on the same immunodominant determinant characterizing the response to native HEL, but further skewed to the Th1 pathway. No difference between HEL and RCM-HEL could be observed in the efficiency of processing, nor in the type of APCs involved. In vivo experiments show that coimmunization with HEL and RCM-HEL generates distinct Th2 or Th1 responses in naive mice, but the two forms of Ag expand the same HEL-specific public clonotype, characterized by the Vbeta8.2-Jbeta1.5 rearrangement, indicating that the populations of naive T cells activated by the two Ag forms overlap. T cells primed by RCM-HEL are restimulated by soluble HEL in vivo, but divert the phenotype of the HEL-specific response to Th1, implying that priming of naive T cells by a structurally modified Ag can induce Th1-type memory/effector T cells more efficiently than native Ag.     

Immunoregulatory pathways in adult responder mice. II. Regulation of delayed-type hypersensitivity responses by GAT-specific suppressor factors present in GAT-tolerant adult responder mice

We studied the effects of T cell extracts from adult responder BALB/c mice tolerized with poly(Glu60Ala30Tyr10) (GAT)-coupled syngeneic spleen cells (GAT-SP) on delayed-type hypersensitivity (DTH), T cell-proliferative (Tprlf), and plaque-forming cell (PFC) responses. Adult responder mice injected i.v. with GAT-SP develop Lyt-1-2+ suppressor T cells (Ts), which suppress the induction of GAT-specific DTH and PFC, but not Tprlf responses. Sonicates from these Ts contain an afferent-acting, soluble factor(s) (GAT-TsFdh) that specifically suppresses the same responses as the intact Ts (i.e., DTH and PFC, but not Tprlf). Immunosorbent chromatography studies were employed to determine the molecular nature of the suppressive material active on both cellular and humoral responses. In both assay systems, GAT-TsFdh was found to bear determinants encoded by the I subregion of the H-2 complex and a receptor(s) for GAT. BALB/c-derived GAT-TsFdh suppressed the induction of GAT DTH in syngeneic BALB/c and H-2-compatible B10.D2, but not in allogeneic C57BL/6 or CBA/Cum, suggesting a possible H-2 restriction in the suppression. It was also shown that one target of functional regulation by GAT-TsFdh is the T helper cell for DTH responses (DTH-Th). The results suggest that similar Ts and TsF regulate humoral and cell-mediated responses, perhaps by affecting a target common to both pathways (e.g., the T helper cell). The resistance of Tprlf responses to suppression by GAT-TsFdh indicates that the effector DTH-Th target is not a major component of the proliferative response. These data are discussed with respect to GAT-specific TsF-regulating PFC responses, which have been identified in nonresponders and in responders tolerized as neonates with GAT.     

The nature of the interaction between suppressor and helper T cells in the response to LDHB

Purified Lyt-1+2+ T cells were depleted of alloreactive cells by BUdR and light treatment, and then were primed in vitro against LDHB presented on allogeneic APC. Such cells could be restimulated by LDHB on the same allogeneic APC, but not by LDHB on APC syngeneic with the T cells. The restimulated T cells suppressed the proliferative response of Lyt-1+2- T cells primed and restimulated by the same antigen. The suppression, which was antigen specific, occurred after a 6-hr co-culture of the suppressor (Tse) and proliferating helper (Th) cells. The successful interaction (as measured by suppression) between allogeneic Th and Tse cells was found to be determined by the restriction specificity but not the MHC haplotype of Th cells, and the MHC haplotype but not the restriction specificity of Tse cells. Thus, suppression occurred only when the Tse cells carried genes controlling the MHC molecules that served as restriction elements for antigen recognition by the Th cells. No evidence could be obtained for the participation of APC in the Tse-Th interaction. The data suggest the interaction is based on the recognition by the Th cell of the antigen presented in the context of MHC molecules controlled by the Tse cell.     

MHC-linked immune response suppression mediated by T cells bearing I-A-encoded determinants

The immune response to chicken egg-white lysozyme (HEL) is actively and specifically regulated by antigen-specific T cell-mediated suppression in mice bearing the H-2b haplotype; the suppression is therefore MHC-linked. In this report, we propose a possible mechanism for MHC-linked suppression of HEL-helper T cells based on expression of I region-encoded cell surface determinants. We determined whether inhibition of anti-HEL antibody responses correlated with expression of serologically detectable I-A-encoded cell surface determinants by antigen-specific helper, suppressor-inducer, or suppressor-effector T cells. It was observed that HEL-suppressor-effector T cells, but not helper or suppressor-inducer T cells, were eliminated after treatment with anti-I-Ab antibody and complement. Furthermore, suppressor-effector T cells co-express Thy-1, Lyt-2, and I-A cell surface antigens. These results raise the possibility that HEL-specific helper T cells become functionally inhibited after recognition of HEL and I-A alloantigen displayed by suppressor-effector T cells. Thus, the interaction between helper and suppressor T cells may be analogous to the mechanism of T cell-B cell interaction.