The immunobiology of the T cell response to Mls-locus-disparate stimulator cells. I. Unidirectionality, new strain combinations, and the role of Ia antigens

The primary mixed lymphocyte reaction of T cells to Mls-locus-disparate stimulator cells differs from that to non-self Ia antigens in several respects. In the present experiments, the unidirectional nature of this response is shown in several strain combinations, including the newly detected Mlsa and Mlsa-like alleles expressed by strains PL/J, RF/J, and SM/J. All of these strains stimulate MHC-identical T cells strongly. In addition, they stimulate a variety of cloned T cell lines specific for Mlsa,d, which can thus be shown to respond to Mlsa,d stimulators of the H-2b,d,k,u, and v haplotypes. Although these results suggest that primary T cell responses to Mlsa,d are unlikely to be MHC restricted, these primary responses are readily inhibited by monoclonal antibodies specific for the I-A and especially the I-E products borne by the stimulator cells, as well as by monoclonal antibodies specific for L3T4a on the responding T cells. This effect of anti-Ia antibodies is not overcome by exogenous interleukin 1. Thus, I-A and especially I-E molecules are centrally involved in the unidirectional primary T cell response to the potently stimulating Mlsa and Mlsd alleles expressed by cells of several different MHC haplotypes.     

The immunobiology of T cell responses to Mls-locus-disparate stimulator cells. III. Helper and cytolytic functions of cloned, Mls-reactive T cell lines

Mls-specific T cell clones derived by limiting dilution were tested for cytotoxic activity in a lectin-dependent 51Cr-release assay. All the T cell clones tested were cytotoxic in such an assay in apparent contrast to previous reports. However, only those target cells sensitive to cytolysis by other L3T4a+ cytolytic T cells were killed by Mls-specific T cell clones in short term 51Cr-release assays, possibly explaining this discrepancy. All the T cell clones tested were L3T4a+, Lyt-2- and stimulated B cells from Mlsa,d strains of mice to proliferate and secrete immunoglobulin. Furthermore, lysis of innocent bystander targets was observed when the T cells were stimulated with Mls-disparate stimulator cells. These results are consistent with those obtained with L3T4a+ T cells specific for protein antigen:self Ia and that express cytotoxic potential.     

Allogeneic mixed lymphocyte reactions in humans: pretreatment of either the stimulator or the responder cell population with monoclonal anti-Ia antibodies leads to an inhibition of cell proliferation

We analyzed the effect of 2 hybridoma monoclonal antibodies (Mab), D1-12 and D4-22, with specificity for common determinants of human Ia molecules, on the mixed lymphocyte culture (MLC) response. The results show that addition of either of the 2 Mab as late as day 3 after the onset of the culture completely inhibits the proliferative response generated in MLC. Because the antigenic determinants recognized by the 2 Mab that were used in this study have been shown to belong to distinct Ia molecules, it appears the inhibitory effect observed in MLC containing such Mabs cannot be explained simply by the masking of Ia molecules on the stimulator cell population. In agreement with previous studies by other investigators, treatment of a leukocyte population with the cytolytic D1-12 Mab plus complement strongly reduced its ability to stimulate in MLC. More importantly such a treatment also decreased the ability of a leukocyte population to respond in MLC. In the latter case, the inhibitory effect appears to be directed against T cells since highly purified E-rosetting cells treated with D1-12 plus complement were unable to respond in MLC. The possible implications of these results are discussed.     

Analysis of T-T lymphocytes and T-accessory cell interactions using cloned T cells: MHC I restricted cloned T cells activate MHC II restricted T helper cells

We evaluated the role of molecules of the major histocompatibility complex (MHC) involved in the cellular interactions of two T-cell clones by testing the effect of monoclonal antibodies on the responses of the clones in vitro. The two T-cell clones used in the study are specific for minor histocompatibility antigens and restricted to the H-2K^k. In the absence of exogenous IL-2 the clones require the presence of Ia⁺, Thy-1⁻ accessory cells and of Thy-1⁺, Lyt-1⁺2⁻ cells in the irradiated spleen cell suspension used as stimulator. It is also necessary that both the accessory cells and the T cells in the stimulator cell populations are recognized specifically by the clones. Monoclonal antibodies specific for the H-2K product inhibited the lytic effector function of the cytolytic clone. These antibodies when added to cultures of stimulator cells and clones inhibited also the proliferation of this clone and of a nonlytic clone. When antigen recognition was measured by the increase in sensitivity of the clones to IL-2 while confronted with uv-irradiated stimulator cells, both clones were blocked efficiently by anti-H-2K antibodies. Thus, these results suggest that the interaction of monoclonal antibodies with the restricting H-2K molecule is sufficient to block the recognition signal, a prerequisite for proliferation. In contrast, monoclonal antibodies specific for A_αA_β and/or E_αE_β had no effect on cytolysis or on restricted recognition. However, they inhibited the proliferative responses as efficiently as the H-2K specific antibodies. Inhibition by class II-specific antibodies was not abolished when stimulator cell populations were depleted of Lyt-2⁺ cells. The blocking effect, however, was reversed by the addition of IL-2. No inhibition was obtained with antibody specific for E_αE_β when B10.A(4R) spleen cells, which do not express E_αE_β, or when B10.A(4R) accessory cells, which were reconstituted with (BALB/c X B10.A(4R)) F1 T cells, were used as stimulators. Stimulator cells heterozygous for H-2 could be inhibited by antibodies to the parental haplotype not encoded in the clones (H-2K^d). These and previous results suggest that H-2K-restricted minor histocompatibility antigen-specific recognition transmits an activating signal to the clones and to the stimulator cells. The clones probably are induced to express more IL-2 receptors. The stimulator T cells seem to interact through A_αA_β and E_αE_β molecules with syngeneic accessory cells. This interaction results in IL-2 production by the stimulator T cells and thus in the proliferation of the clones.     

Mouse T lymphocytes proliferative responses specific for human MHC products in mouse anti-human xenogeneic MLR

It has been reported that human T cells recognize the polymorphism of murine Ia antigens in the human anti-mouse xenogeneic mixed lymphocyte reactions (MLR). In this study, murine T cell recognition of human Class II antigens of the major histocompatibility complex (MHC) was analyzed in mouse anti-human xenogeneic MLR responses. The xenoreactive murine T cell proliferative response was blocked by adding anti-HLA-DR monoclonal antibody to the xenogeneic MLR culture. The specificity of xenoreactive murine T cells was examined with regard to the secondary and tertiary xenogeneic MLR system. The xenoreactive murine T cells were restimulated by distinct human stimulator cells that had no shared HLA antigens with the stimulator used in the primary MLR. The data presented here show that the murine xenoreactive T cells recognize the shared determinant(s) of HLA-DR antigen on non-T, non-B stimulator cells. The xenoreactive murine T cell proliferative responses were mediated by Thy-1+, Lyt-1+, and Lyt-2- cells. Furthermore, the xenoreactive T cell responses required Ia+ cells, and Ia antigen on accessory cells plays a crucial role in eliciting the xenoreactive responses against human stimulator cells, while Ia+ accessory cells in the responding cell population are not essential for the elicitation of allogeneic MLR responses, as reported previously.     

Minor lymphocyte stimulatory antigen-bearing stimulator cells require lipopolysaccharide activation to induce programmed cell death in T cell hybridomas.

T cell hybridomas respond to conventional peptide Ag associated with self major histocompatibility restriction elements, as well as to alloantigens, activating lectins, and stimulatory forms of mAb by producing lymphokines and undergoing programmed cell death (PCD). We show here that the level of PCD and IL-2 production correlate well in responses to CD3 or allostimulation. The response to minor lymphocyte-stimulatory (Mls) Ag, members of the family of endogenous superantigens, however, are marked by divergence in the levels of the PCD and lymphokine responses. Specifically, PCD in response to Mls activation is achieved poorly despite vigorous IL-2 production. B lymphoma cell stimulators induced PCD in alloreactive T cell hybridomas but not in Mls-reactive T cell hybridomas. This suggests that the absence of PCD in the Mls response is a function of superantigen recognition rather than the stimulator cell type. LPS-preactivated Mls+ stimulators, either splenic B or B lymphoma cells, are shown to trigger PCD in the T cell hybridomas. These results imply that T cell interaction with Mls presented by untreated stimulator cells is not sufficient for induction of PCD and thus is distinct from interactions with conventional Ag.     

Endowing T cells with antibody specificity using chimeric T cell receptors.

T cells recognize antigen in the form of a peptide associated with a cell surface molecule encoded by the major histocompatibility gene complex (MHC). The elaborate requirements for the T cell receptor (TCR)-antigen interaction stand in contrast to the simple and defined nature of the antigenic determinants recognized by antibodies. The similarity in the molecular structure and gene organization between antibodies and the TCR has prompted attempts to interchange the antigen-binding, variable regions of these molecules. To this end, chimeric TCR (cTCR) genes, composed of the variable domains of antibodies linked to TCR constant regions, have been used to confer antibody-type specificity on T cells. cTCR-expressing T cells respond to stimulator cells as well as to immobilized antigen in an MHC unrestricted and independent manner. The antibody-like specificity of the resulting T cells has been exploited, using defined ligands, to elucidate the physicochemical parameters that govern TCR-mediated signaling, and to provide a useful experimental system to study the role of MHC and cell-adhesion/accessory molecules in T cell activation. The successful expression of such cTCR in transgenic mice opens new avenues to explore the role of the MHC in T cell development and maturation. Eventually, chimeric receptors specific to tumor or viral antigens might be used for in vivo targeting of T cells in the framework of immuno- and gene therapy.     

Antigen-binding receptors on T cells from long-term MLR. evidence of binding sites for allogeneic and self-MHC products

Antibody inhibition of radiolabelled stimulator membrane vesicle binding by T blasts activated in the mixed lymphocyte reaction (MLR) was used to identify responder-cell determinants involved in the binding phenomenon. Antisera or monoclonal antibodies against Thy-1, Lyt-1, Lyt-2 and Ly-6 antigens were not inhibitory. However, antibodies against heavy-chain V region (VH) determinants strongly inhibited vesicle binding by both primary and long-term MLR blasts. Anti-Ia (both alloantisera and monoclonal reagents) caused inhibition of antigen binding by primary MLR blasts only. T blasts from long-term MLR lines were neither Ia-positive, nor susceptible to blocking of antigen binding with anti-Ia. However, these cells were capable of specifically absorbing soluble syngeneic Ia material, with the concomitant appearance of vesicle-binding inhibition with anti-Ia sera. Acquisition of syngeneic Ia by T blasts was effectivelly blocked with the anti-VH reagent. Passively bound self-Ia did not interfere with vesicle binding in the absence of anti-Ia. These results strongly suggest the existance of specific self-Ia acceptor sites closely linked to the receptors for stimulator alloantigens on T cells proliferating in MLR. A receptor model based on these findings is briefly discussed.     

T lymphocyte heterogeneity in the rat. III. Autoreactive T cells are activated by B cells

Evidence has been presented to show that CD4+ autoreactive T cell lines (ATs)2 in the rat require periodic stimulation with syngeneic spleen cells for in vitro proliferation. This proliferation can be blocked by treatment of the stimulator (spleen) cells with mAb to Ia antigens. Although ATs are Ia+ and can activate the allogeneic MLR, they fail to be autostimulatory. Fractionation of the spleen cells revealed that ATs can be stimulated with B cells and not by macrophages, although the latter were efficient in several accessory cell functions, including antigen presentation, lectin-dependent T cell activation and allogenic MLR response. Moreover, B cells proliferated and differentiated in response to AT cells. These data are compatible with a model in which ATs respond to hitherto undetermined B cell membrane antigen(s) in association with MHC class II antigens. These results may have important implications in understanding autoimmune responses.     

Nature of the antigenic complex recognized by T lymphocytes. IV. Inhibition of antigen-specific T cell proliferation by antibodies to stimulator macrophage Ia antigens.

We have previously demonstrated that nonimmune guinea pig T lymphocytes could be specifically sensitized with TNP-modified allogeneic macrophages after eliminating the alloreactive T cells with bromodeoxyuridine (BUdR) and light treatment. This procedure allowed the unique opportunity to use anti-Ia sera directed against the Ia antigens of only the stimulator macrophages or responder T cells to determine against which cell type anti-Ia would block TNP-specific stimulation. It was found that the TNP-specific DNA synthetic response of BUdR and light-treated T cells stimulated with TNP-modified allogeneic macrophages was totally eliminated by anti-Ia sera directed solely against the allogeneic stimulator macrophage. In contrast, anti-Ia sera directed only against the responder T cells had no effect on their response to TNP-modified allogeneic macrophages. These findings indicate that macrophage Ia antigens are required for efficient T cell-macrophage interactions and raise the possibility that T cell Ia antigens may not be required for collaboration with macrophages. This latter possibility was substantiated by experiments in which we show that treating T cells with anti-Ia sera and complement to remove the Ia-positive cells either before or after priming, or both, had no effect on their ability to be primed and restimulated with TNP-modified macrophages.     

Activation requirements of cloned inducer T cells. III. Need for two stimulator cells in the response of a cloned line to Mls determinants

To gain insight into the nature of Mls determinants, we examined the stimulator cells responsible for the activation of inducer T cell clones by Mls determinants. Two types of clones responding to Mls determinants were identified. One type responded to purified B cells, but not to splenic adherent cells (SAC), from mice bearing Mls stimulatory determinants. The other type of Mls-reactive T cell clone, including the representative clone Ly1-N5, demonstrated a vigorous response to unfractionated spleen cells, but showed little or no response to B cells alone or to SAC alone from mice bearing the Mlsa or Mlsd stimulatory determinant. The response of these clones to Mls determinants required stimulation by two cell types. The failure of clone Ly1-N5 to respond to Mlsa-bearing B cells was reversed by the addition of SAC taken from mice bearing the Mlsa allele. In addition, SAC from mice bearing the nonstimulatory Mlsb allele could synergize with B cells from Mlsa-bearing animals. B cells were required to provide the Mlsa determinant, because the combination of Mlsa-bearing SAC and Mlsb-bearing B cells did not activate the clone. The response of clone Ly1-N5 to Mls is restricted by Ia determinants (shared by H-2b, H-2d, and H-2k haplotypes but not by the H-2q haplotype). The permissive H-2 alleles can be present either on the stimulator B cell or on the SAC. The optimal response of the clone was obtained by using B cells bearing Mlsa and the permissive Ia epitopes. However, a significant response of the clone to B cells bearing Mlsa but an inappropriate Ia (Iaq) was also seen in the presence of SAC bearing the nonstimulatory Mlsb allele but the permissive Ia epitopes.     

Antigen-binding receptors on T cells from long-term MLR. Evidence of binding sites for allogeneic and self-MHC products

Antibody inhibition of radiolabelled stimulator membrane vesicle binding by T blasts activated in the mixed lymphocyte reaction (MLR) was used to identify responder-cell determinants involved in the binding phenomenon. Antisera or monoclonal antibodies against Thy-1, Lyt-1, Lyt-2 and Ly-6 antigens were not inhibitory. However, antibodies against heavy-chain V region (V_H) determinants strongly inhibited vesicle binding by both primary and longterm MLR blasts. Anti-Ia (both alloantisera and monoclonal reagents) caused inhibition of antigen binding by primary MLR blasts only. T blasts from long-term MLR lines were neither Ia-positive, nor susceptible to blocking of antigen binding with anti-Ia. However, these cells were capable of specifically absorbing soluble syngeneic Ia material, with the concomitant appearance of vesiclebinding inhibition with anti-Ia sera. Acquisition of syngeneic Ia by T blasts was effectively blocked with the anti-V_H reagent. Passively bound self-Ia did not interfere with vesicle binding in the absence of anti-Ia. These results strongly suggest the existance of specific self-Ia acceptor sites closely linked to the receptors for stimulator alloantigens on T cells proliferating in MLR. A receptor model based on these findings is briefly discussed.Abbreviations used in this paper B10 C57BL/10 - Con A concanavalin A - FcR Fc receptor - FCS fetal calf serum - H heavy chain - Ia I-region associated antigen - Ig immunoglobulin - LPS lipopolysaccharide - Lyt T-lymphocyte differentiation antigen - MHC major histocompatibility complex - MLR mixed lymphocyte reaction - PM plasma membrane - T thymus derived - Tcr T-cell receptor - V variable region of Ig     

Possible involvement of the T4 molecule in T cell recognition of class II HLA antigens: evidence from studies of proliferative responses to SB antigens

The T4 molecule has been identified as a marker of human T cell differentiation, but the function of this molecule remains to be defined. We have investigated its possible functional involvement in T cell proliferative responses to class II HLA antigens encoded by the recently described SB locus. The responses of SB-primed cells (specific for each of four different SB antigens) were studied with the use of two proliferation-inducing stimuli, SB antigen or TCGF. The proliferative responses to both stimuli were found to be mediated by T4+, T8- cells. Monoclonal antibodies against some epitopes on the T4 molecule (OKT4A and OKT4B) substantially blocked antigen-stimulated proliferative responses; antibodies against other epitopes of the T4 molecule (OKT4, T4C, T4D) blocked less well. Inhibition of SB-specific proliferation by antibodies to the T4 molecule was maximal only when the antibodies were incubated with the responder cells before the addition of stimulator cells. Proliferative responses of SB-primed cells stimulated with TCGF alone were not inhibited by any of the OKT4-related antibodies, but were completely inhibited by the anti-Tac monoclonal antibody, which reacts with the TCGF receptor. These results lend further support for the hypothesis that the T4 molecule is involved in T cell recognition of and/or activation by class II HLA antigens. We suggest that 1) the T4 molecule binds a nonpolymorphic epitope on class II HLA molecules, and 2) this interaction may facilitate, but not be an obligate requirement for, T cell activation by class II antigens.     

Artificial T cell:B cell conjugation. A unique approach to analyze weak cell-cell interactions

An antibody response against a thymic-dependent Ag requires cognate recognition of the Ag by B and T cells. Functional T-B cell (T-B) interaction involves binding of Ag by B cell surface Ig, internalization and processing of Ag, expression of an Ag fragment in the context of Ia, binding of Ag/Ia by the TCR and binding of T cell-derived lymphokines by B cell lymphokine receptors. It is becoming increasingly evident that B and T cell accessory molecules also are involved in T-B interactions. To determine the role of accessory molecules in T-B collaboration, we have designed a system in which T-B interaction was artificially induced in the absence of carrier protein. TNP-modified, turkey gamma-globulin-specific, Th cells were allowed to form conjugates with TNP-specific B cells in the absence of hapten-carrier complex. Both B and T cells were induced to proliferate and B cells partially differentiated into antibody-secreting cells when B cells were cultured with TNP-modified but not unmodified T cells. The activation of B cells by TNP-modified T cells was not MHC restricted but was blocked by anti-Ia antibodies, suggesting a role for Ia distinct from Ag presentation. Furthermore, B cell proliferation was also inhibited by antibodies to L3T4 and LFA-1, suggesting a functional accessory role for these molecules in induction of B cell proliferation/differentiation.     

The role of Ia molecules in the activation of T lymphocytes. II. Ia-restricted recognition of allo K/D antigens is required for class I MHC-stimulated mixed lymphocyte responses

The role of Ia molecules in the T cell proliferative response to class I (H2K/D) MHC alloantigens was examined. Proliferation in response to allo-K/D antigenic stimulation, but not to allo-Ia, was markedly inhibited by the addition of monoclonal anti-responder Ia antibodies to cultures in the absence of C. This anti-Ia blocking was observed in responses against both allelic and mutant class I antigens. Partial blocking was observed by using an anti-I-A or anti-I-E monoclonal antibody alone, whereas marked inhibition was seen with these two reagents together when the proliferating cells derived from a responder strain expressing both IA and IE gene products. Syngeneic Ia molecules appear to function as restriction elements, because they are required even in the presence of a source of exogenous second signal, phorbol myristic acetate or IL 1. The K/D-specific response required a responding cell that bears both Lyt-1 and -2 antigens, whereas responses generated to alloantigenic differences, including the I region, require only an Ly-1+ cell. The implications of these data with respect to the repertoire of the alloreactive proliferating T cell and the expression of the Lyt-2 antigen by such cells are discussed.     

Sodium periodate-induced T cell mitogenesis: an analysis of the requirement for Ia and IL 1

T lymphocytes oxidized with the mitogen sodium periodate undergo a proliferative response when cultured in the presence of Ia+ accessory cells. However, the exact role(s) the accessory cells play in such a response has not been clearly defined. We have evaluated the role of Ia and the requirement for interleukin 1 (IL 1) in periodate mitogenicity by using the Ia+ cloned tumor cell lines P388AD (Ia+, IL 1 inducible) and P388NA (Ia+, IL 1 noninducible) as accessory cells. P388AD but not P388NA was able to supply accessory cell function to periodate-treated T cells, suggesting that Ia expression alone was not sufficient to reconstitute a response. Monoclonal anti-I-Ad and anti-I-Ed antibody blocked the accessory cell function of P388AD. In addition, monoclonal antibody GK 1.5, directed against the T cell determinant L3T4a, blocked the P388AD/periodate-treated T cell interaction, confirming that this interaction was restricted by class II molecules. Although Ia expression was required, the response was not major histocompatibility complex (MHC) restricted, because allogeneic as well as syngeneic macrophages were capable of supplying accessory cell function to periodate-treated T cells. Exogenous IL 1 alone was able to trigger periodate-treated T cells, suggesting that Ia was required for the induction of IL 1 synthesis by the accessory cells. Furthermore, purified IL 2, devoid of IL 1 activity, was able to fully reconstitute the proliferative response of accessory cell-depleted oxidized T cells to a level equal to that of whole spleen accessory cells or P388AD. These data suggest that periodate-treated T cells can proliferate with IL 1 alone and that Ia+ accessory cells in periodate-mediated T cell mitogenicity may function in the release of IL 1 and the induction of IL 2 synthesis by the T cells.     

Stimulator cell requirements for allospecific T cell subsets: specialized accessory cells are required to activate helper but not cytolytic T lymphocyte precursors

Murine cortisone-resistant thymocytes were separated by staining with monoclonal anti-Lyt-2 antibody and FMF into Lyt-2- and Lyt-2+ subsets in order to analyze the nature of stimulator accessory cells required to activate each of these functionally distinct T cell subpopulations. The Lyt-2- fraction was able to proliferate but not to generate cytotoxic cells when stimulated by irradiated allogeneic spleen cells. Fractionation of the stimulator population showed that low numbers of dendritic cells and splenic macrophages, but not equivalent numbers of whole spleen cells or peritoneal macrophages, were able to stimulate the Lyt-2- population. On the other hand, the Lyt-2+ population, which showed little if any proliferation in response to irradiated spleen cells, contained all the precursors of cytolytic T lymphocytes. In contrast to the highly specific stimulator requirement of the Lyt-2- fraction, allospecific cytotoxic cells were generated from Lyt-2+ cells by any alloantigen-bearing stimulator cell provided interleukin 2 was present. This was confirmed by limiting dilution analysis: alloreactive CTL-P frequencies in spleen and thymus were not influenced by the nature of the stimulator cell. These data collectively indicate that heterogeneous Ia+ accessory cells are required to stimulate helper but not cytolytic T cell precursors.     

Role of L3T4 and Ia in the heteroclitic response of T cells to cytochrome c

The activation of helper T lymphocytes has been proposed to result from the sum of low-affinity interactions between the specific immune receptor, as well as nonpolymorphic receptors such as L3T4 on the T cell surface, and nominal antigen and Ia displayed in a multivalent array on the antigen-presenting cell surface. The present work takes advantage of a T cell hybridoma specific for pigeon cytochrome c in the context of I-Ek, which responds to tobacco hornworm moth cytochrome c at one hundredth the concentration of the homologous antigen, to determine if the T cell's requirement for L3T4 and Ia is directly related to its functional affinity for antigen. The results demonstrate that the T cell's activation by pigeon cytochrome c was blocked by antibodies directed to L3T4 and to I-Ek, even at antigen concentrations twofold to fourfold above those required for maximal responses. In contrast, the response to tobacco hornworm moth cytochrome c was not as affected by these antibodies under equivalent superoptimal conditions. The same phenomenon was observed for the T cell's activation by the carboxyl-terminal peptide fragments of the two cytochromes c, which do not require processing, indicating that the differences were not due to the relative efficiency of processing and/or presentation of the antigens. Although both I-Ek- and L3T4-specific antibodies blocked the T cell response to pigeon cytochrome, antibodies to I-Ak had no effect, even though I-Ak had been considered to be a ligand for L3T4. Thus, either Ia does not bind L3T4 or, if it does, I-Ek must be a sufficient ligand for L3T4 for T cells that recognize their antigen in the context of I-Ek. These studies provide more definitive evidence that the T cell's requirement for the functions of Ia and of L3T4 is dependent on the T cell's functional affinity for its antigenic determinant. This data is consistent with a model of T cell activation in which, given a high enough affinity of the T cell receptor for the processed antigen, the requirement for other components of a stimulatory complex, such as Ia and L3T4, may diminish to undetectable levels.     

Analysis of Ir gene function using monoclonal antibodies: independent regulation of GAT and GLPhe T cell responses by I-A and I-E subregion products on a single accessory cell population

T cell proliferative responses to the synthetic polypeptides GAT and GLPhe are under Ir gene control. GAT responses are regulated by gene(s) in the I-A subregion, and GLPhe responses are controlled by a pair of complementing genes mapping to the I-A and I-E subregions. We demonstrate that monoclonal antibody to the I-A gene product inhibits GAT proliferation but not the GLPhe response, whereas a monoclonal antibody to the I-E associated Ia-7 determinant inhibits GLPhe but not GAT proliferation, which indicates independent involvement of each Ia determinant in antigen presentation for the T cell response to these antigens. Use of the same subregion-specific monoclonal antibodies in complement-dependent lysis demonstrates that the antigen-presenting cells for GAT and GLPhe express both I-A and I-E products. The possibility that an Ia subregion-specific "self-receptor" functions on the reactive T cells as a regulatory element is discussed.     

Activation requirements for normal T cells: accessory cell-dependent and -independent stimulation by anti-receptor antibodies

We have examined the requirements for the activation of normal T cells by two anti-T cell receptor antibody preparations, including a rabbit antiserum, R3497, which binds to all normal T cells, and a rat monoclonal antibody, KJ16-133, which binds to about 20% of T cells. The requirements for stimulation of T cells by both antibodies were similar. Soluble antibodies in the absence of accessory cells (AC) failed to induce either proliferation or the expression of IL 2 receptors, and the addition of either IL 2 or PMA failed to synergize with these soluble antibodies for an AC-independent proliferative response. Activation could only be achieved in the presence of Fc receptor-positive AC, although Fc receptor expression alone appeared not to be sufficient for AC activity because some Fc receptor-positive cells did not function in this capacity. Activation with anti-receptor antibody conjugated to Sepharose 4B beads could be demonstrated in the presence of some exogenous cofactors, such as IL 2 and PMA, but not in the presence of recombinant IL 1. When activation by soluble antibody plus AC was compared to activation by bead-conjugated antibody + recombinant IL 2, it was found that the former favored the stimulation of Lyt-2+ cells. The effects of the addition of anti-L3T4 monoclonal antibody was also examined in this system. Anti-L3T4 inhibited the response of L3T4+ cells when used in the presence of Ia+ as well as Ia- AC, and it also inhibited activation in a system in which KJ16-133 conjugated to Sepharose was used in the absence of AC. Because anti-L3T4 had an inhibitory effect in the presence of Ia- AC as well as in the absence of any AC, it is concluded that L3T4 does not necessarily function by interacting with Ia on the surface of AC, and may directly transmit down-regulatory signals when bound by anti-L3T4.