Antigen presentation by chemically modified splenocytes induces antigen-specific T cell unresponsiveness in vitro and in vivo.

We investigated the antigen specificity and presentation requirements for inactivation of T lymphocytes in vitro and in vivo. In vitro studies revealed that splenocytes treated with the crosslinker 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (ECDI) and soluble antigen fragments failed to stimulate significant proliferation by normal pigeon cytochrome c-specific T cell clones, suggesting that the chemical treatment inactivated full antigen presentation function. However, T cell clones exposed to ECDI-treated splenocytes and antigen in vitro were rendered unresponsive for at least 8 d to subsequent antigen stimulation with normal presenting cells. As predicted by the in vitro results, specific T cell unresponsiveness was also induced in vivo in B10.A mice injected intravenously with B10.A, but not B10.A(4R), splenocytes coupled with pigeon cytochrome c via ECDI. The antigen and MHC specificity of the induction of this T cell unresponsiveness in vitro and in vivo was identical to that required for T cell activation. These results suggest that nonmitogenic T cell recognition of antigen/MHC on ECDI-modified APCs results in the functional inactivation of T cell clones.

Gene complementation. Neither Ir-GLphi gene need be present in the proliferative T cell to generate an immune response to Poly(Glu55Lys36Phe9)n.

The cellular requirements for immune response (Ir) gene expression in a T cell proliferative response under dual Ir gene control were examined with radiation-induced bone marrow chimeras. The response to poly(Glu55Lys36Phe9)n (GLphi) requires two responder alleles that in the [B10.A X B10.A(18R)]F1 map in I-Ab and I-Ek/Cd. Chimeras in which a mixture of the nonresponder B10.A parental cells (which possess only I-Ek/Cd) and the nonresponder B10.A(18R) parental cells (which possess only I-Ab) were allowed to mature in a responder F1 environment did not respond to GLphi, which suggests that at least one cell participating in the response needed to possess both responder alleles to function. When T cells from such A + 18R leads to F1 chimeras were primed in the presence of responder antigen-presenting cells (APC), the chimeric T cells responded to GLphi, which suggests that both responder alleles must be expressed in the APC but not necessarily in the T cell. Interestingly, acutely irradiated F1 animals were found not to be an adequate source of responder APC for priming the proliferating T cell because of the rapid turnover of peripheral APC after irradiation. In adoptive transfer experiments, T cell-depleted bone marrow had to be used as a source of responder APC. When bone marrow cells from (B10.A X B10)F1 responder animals were allowed to mature in a low-responder B10 of B10.A parental environment, neither chimera, F1 leads to A or F1 leads to B, could respond to GLphi. This demonstrated that the presence of high-responder APC, which derive from the donor bone marrow, was not sufficient to generate a GLphi response. It appears that in addition it is essential for the T lymphocytes to mature in a high-responder environment. Finally, B10.A(4R) T cells, which possess neither Ir-GLphi responder allele, could be educated to mount a GLphi-proliferative response provided that they matured in a responder environment and were primed with APC expressing both responder alleles. Therefore, the gene products of the complementing Ir-GLphi responder alleles appear to function as a single restriction element at the level of the APC. T cells that do not possess responder alleles are not intrinsically defective, because they could be made phenotypic responders if they developed in an environment in which responder major histocompatibility complex (MHC) products were learned as self and if antigen was presented to them by APC expressing responder MHC products.

A quantitative analysis of antigen-presenting cell function: activated B cells stimulate naive CD4 T cells but are inferior to dendritic cells in providing costimulation.

Ligation of CD28 on CD4 Th1 clones and freshly isolated mixtures of naive and memory CD4 T cells triggered their T cell receptors (TCR) is sufficient to induce the costimulatory signals necessary for interleukin 2 (IL-2) production by these cells. CTLA-4-reactive ligands expressed on antigen-presenting cells (APC) are critical in providing costimulatory signals to these T cell populations. We demonstrate that these activation characteristics apply equally to purified naive CD4 T cells. Because B cell blasts express CTLA-4-reactive ligands and high levels of adhesion and major histocompatibility complex class II molecules, they would be expected to engage both the TCR and CD28 and consequently stimulate IL-2 production by naive CD4 T cells. Using purified populations of cells in limiting dilution cultures, we have carried out a quantitative analysis of the interaction between naive CD4 T cells and either activated B or dendritic cells. We demonstrate that B cell blasts stimulate a high frequency of naive CD4 T cells. Slight differences in TCR signaling efficiency between the two APC types were observed. Even at optimal peptide concentrations, however, the amount of IL-2 made by individual T cells was fourfold lower in response to B cell blasts than to dendritic cells. This relative deficiency of activated B cells was due to their inability to optimally costimulate naive CD4 T cells.

Anergy and cytokine-mediated suppression as distinct superantigen-induced tolerance mechanisms in vivo.

Recombinant-activating gene 2 (RAG-2-/-) T cell receptor-transgenic mice repeatedly injected with the superantigen staphylococcal enterotoxin A entered a tolerant state in which splenic CD4+ T cells produced little interleukin (IL)-2, interferon gamma, or IL-4. This state resulted from a combination of both clonal anergy and cytokine-mediated immunosuppression. The anergy persisted for at least 3 wk and could be distinguished from the suppression by a decrease in IL-2 production per cell, a block in the activation of early response kinases, and a failure to be reversed with anti-transforming growth factor (TGF)-beta. Full suppression lasted for only 1 wk and involved both IL-10 and TGF-beta, but required additional unknown molecules for optimal effect. These experiments show that complex in vivo interactions of multiple peripheral tolerance mechanisms can now be dissected at both the cellular and molecular levels.

T-lymphocyte-enriched murine peritoneal exudate cells. II. Genetic control of antigen-induced T-lymphocyte proliferation.

The recent introduction of a reliable, T-lymphocyte proliferation assay, which utilizes thioglycollate-induced, nylon wool column-passed, peritoneal exudate lymphocytes from immune mice (PETLES), allowed us to investigate the genetic control of murine immune responses at the T-lymphocyte level. Examination of the blast cells generated in this population 5 days after stimulation with antigen, revealed that 85% of the cells bore the Thy 1 antigen on their surface, whereas only 5% bore immunoglobulin. Thus, the assay can be considered to measure almost exclusively T-lymphocyte function. This assay was used to examine the T-lymphocyte proliferative responses to seven different antigens: poly(Glu60Ala30Tyr10), poly(Glu58Lys38Tyr4), poly-(Tyr,Glu)-poly-D,L-Ala--poly-Lys, poly-(Phe,Glu)-poly-D,L-Ala--poly-Lys, staphylococcal nuclease, lactate dehydrogenase H4, and the BALB/c IgA myeloma protein, TEPC-15. PETLES from a large number of different inbred mouse strains, including H-2 congenic resistant lines and H-2 recombinants, were studied. The strains could be classified as high responders, low responders, or nonresponders to a particular antigen as judged by the magnitude of the T-lymphocyte proliferative response. In every case but one this classification corresponded to the responder status given the strain based on its ability to mount an in vivo antibody response to the same antigen. For two of the antigens, poly-(Tyr,Glu)-poly-D,L-Ala--poly-Lys and TEPC-15, the immune response genes controlling the T-lymphocyte proliferative response were mapped to the K region or I-A subregion of the major histocompatibility complex, as had previously been shown for the control of the antibody responses to these antigens. This tight linkage of the two phenotypic responses very strongly suggests that the same immune response gene controls the expression of both the proliferative and antibody responses. Since there is essentially no contribution from B lymphocytes in the T-lymphocyte proliferation assay, it seems reasonable to conclude that none of the seven immune response genes studied are expressed solely in B lymphocytes.

Antigen presentation in the murine T-lymphocyte proliferative response. I. Requirement for genetic identity at the major histocompatibility complex.

A method is described for stimulating proliferation in primed populations of murine T lymphocytes using antigen bound to mitomycin-C-treated spleen cells. This form of antigen presentation appears to be an active process because heat-killed spleen cells are ineffective, and because genetic similarity at the major histocompatibility complex (MHC) between the responder T cells and the presenting spleen cells is required for effective interactions. At all times examined, from day 3 to day 6 of the proliferative response, syngeneic spleen cells presented antigen better to peritoneal exudate T-lymphocyte-enriched cells (PETLES) than semisyngeneic F(1) spleen cells, which in turn could present antigen better than totally allogeneic spleen cells. Spleen cell mixing experiments demonstrated that these genetic restrictions were not the result of suppression by the ongoing mixed lymphocyte reactions (MLR) in the allogeneic and F(1) cases. Furthermore, incompatibility at the Mls locus generated a strong MLR but failed to prevent antigen presentation if the spleen cells and PETLES were compatible. Genetic mapping studies demonstrated that compatibility at only the I-A subregion of the MHC was sufficient for effective presentation of the antigen, dinitrophenylated ovalbumin. Compatibility at only the K region, or the K and D regions was not sufficient. These results support the concept that functional activation of primed, proliferating T lymphocytes requires the participation of gene products coded for by the I region of the MHC. This conclusion is consistent with a growing body of evidence which suggests that most T cells recognize antigen in association with MHC gene products.

Gene complementation in the T-lymphocyte proliferative response to poly (Glu55Lys36Phe9)n. A demonstration that both immune response gene products must be expressed in the same antigen-presenting cell.

The immune response (Ir) to the random copolymer GLphi depends upon the function of two Ir genes, Ir-GLphi-beta[beta] and Ir-GLphi-alpha[alpha], mapped to the I-A and I-E/C subregions of the major histocompatibility complex, respectively. In this paper, the site(s) of expression of the products of these two Ir genes was examined by evaluating T-lymphocyte proliferative responses of bone marrow radiation chimeras. Chimeras were created in [alpha+beta- X alpha-beta+]F1 responder mice by lethal irradiation and reconstitution with a mixture of bone marrow cells from both parental strains. These chimeras failed to respond to GLphi, although they were capable or responding to the much weaker antigens, (T,G)-A--L, TEPC-15, pigeon cytochrome c, and (H,G)-A--L. This failure to respond to GLphi was shown not to be the result of a cryptic mixed lymphocyte reaction, as similar chimeras created in (alpha+beta+ X alpha-beta+)F1 mice responded well to GLphi, although they possessed almost the same potential histoincompatibility. Furthermore, the lack of response to GLphi could not be attributed to a general failure of the two parental cell types in the chimeras to collaboratc with each other, as each chimeric parental cell type could respond to dinitrophenyl conjugated ovalbumin presented on nonimmune spleen cells from the other parent. Thus, the failure of low responder parental into F1 high responder chimeras to generate an immune response to GLphi suggests that immune competence for this antigen requires at least one cell type in the immune system to express gene products of both the Ir-glphi-alpha and -beta genes, i.e. one cell must be of high responder genotype. The the antigen-presenting cell is one such cell type was shown by experiments in which GLphi-primed T lymphocytes from responder F1 mice were stimulated with antigen bound to nonimmune spleen cells. Only spleen cells from responder F1 and recombinant mice could present GLphi. Neither of the two complementing nonresponder parental spleen cell populations, either alone or mixed together, could present GLphi, although both could present purified protein derivative of tuberculin. This was shown to be the case for T cells positively selected in vitro as well as freshly explanted T cells. Thus, both Ir-GLphi-alpha and Ir-GLphi-beta gene products must be expressed in the same antigen-presenting cell to generate a T-lymphocyte proliferative response to GLphi. The implications of these findings for models of two gene complementation are discussed.

T-lymphocyte response to cytochrome c. I. Demonstration of a T-cell heteroclitic proliferative response and identification of a topographic antigenic determinant on pigeon cytochrome c whose immune recognition requires two complementing major histocompatibility complex-linked immune response genes.

The T-lymphocyte proliferative response to pigeon cytochrome c was studied in the mouse. H-2a and H-2k strains were responders to this antigen whereas H-2b, H-2d, H-2f, H-2ja, H-2p, H-2q, H-2r, H-2s, and H-2u strains were low or nonresponders. Genetic mapping demonstrated that two major histocompatibility complex (MHC)-linked Ir genes control the response, one in I-A, the other in I-E/I-C. The major antigenic determinant recognized in this response was localized by cross-stimulations with species variants and cyanogen bromide cleavage fragments of cytochrome c. It was found to be a topographic surface determinant composed of an isoleucine for valine substitution at residue 3, a glutamine for lysine substitution at residue 100 and a lysine for glutamic acid substitution at residue 104. Tobacco hornworm moth cytochrome c, which contains a glutamine at residue 100 but a terminal lysine at residue 103 (one amino acid closer to the glutamine), stimulated pigeon cytochrome c immune T cells better than the immunogen. This result demonstrates for the first time a functional T-cell heteroclitic proliferative response in a system under Ir gene control. Immunization with the cyanogen bromide cleavage fragments revealed that only pigeon cytochrome c fragment 81-104 was immunogenic. This fragment primed for a T-cell proliferative response whose specificity was nearly identical to that of the T-cell response primed for by the whole molecule, suggesting that the glutamine at 100 and the lysine at 104 form the immunodominant portion of the antigenic site. Furthermore, mixing experiments using the two cross-reacting antigens, hippopotamus cytochrome c and Pekin duck or chicken cytochrome c fragment (81-104), each of which contains only one of the two immunodominant substitutions, demonstrated that the T lymphocytes responding to the major antigenic determinant comprise a single family of clones that recognize both amino acids as part of the same determinant. Thus, two complementing MHC-linked Ir genes can control the immune response to a single antigenic determinant.

The requirement for two complementing Ir-GLphi immune response genes in the T-lymphocyte proliferative response to poly-(Glu53Lys36Phe11).

The antibody response to poly-(Glu53Lys36Phe11) (GLphi) has been shown to be under the control of two independent, major histocompatibility-linked immune response genes, designated alpha and beta. In the present work we demonstrate that the T-lymphocyte proliferative response is also under the control of these two immune response genes. Thus, mice of the H-2a, H-2b, H-2k, and H-2s haplotypes were all nonresponders to GLphi. In contrast F1 hybrids between these strains, such as (B10 X B10.A)F1 and (C3H X SJL)F1, as well as several recombinant mice derived from the nonresponder haplotypes, such as B10.1(5R), B10.HTT, and B10.S(9R), were all responders to GLphi. The complementation between nonresponder genomes appeared to be stronger in the cis position than in the trans position for some strain combinations. The failure of strains bearing only one of the two responder alleles to show a T-lymphocyte proliferative response to GLphi, argues strongly that neither gene can be expressed exclusively in B lymphocytes. This conclusion is discussed in relation to another two gene model which has recently been proposed.

Murine syngeneic mixed lymphocyte response. I. Target antigens are self Ia molecules.

A system has been described that produces a murine syngeneic mixed lymphocyte response (MLR) comparable in magnitude to an allogeneic MLR. The responder cells in these cultures exhibit the classic immunologic characteristics of both memory and specificity. Studies using radiation-induced bone marrow chimeras of F(1) {arrow} parent type indicated that, similar to many other T cell-mediated immune responses, the response of the T lymphocytes in the syngeneic MLR was major histocompatibility complex-restricted and was determined by the environment in which the T cells matured. Using responder T cells from F(1) {arrow} parent chimeras and stimulator cells from H-2 recombinant strains, it was possible to map the genes involved in the stimulation to the K and/or I regions. In addition, blocking studies with monoclonal anti-Ia antibodies suggested that in the B10.A strain the critical molecules were products of both the I-A(k) and I-E(k) subregions. The issue of whether the syngeneic MLR is directed solely at self I-region antigens or whether the response represents proliferation to an unknown antigen in association with self I-region determinants was also addressed. Secondary syngeneic MLR were successfully performed in normal mouse serum and with stimulator cells prepared in the absence of bovine serum albumin to rule out the possibility that xenogeneic serum antigens were involved in the stimulation. The possibility that the syngeneic MLR might represent a secondary response to environmental antigens was eliminated by using germ- free mice as a source of stimulator cells and by demonstrating that spleen cells from unimmunized, fully allogeneic chimeras (B10.A {arrow} B10) could generate a normal syngeneic MLR even though such chimeras could not be primed to respond to any foreign antigens unless supplemented in vivo with a source of antigen-presenting cells syngeneic to the B10 host. The possibility that the syngeneic MLR was a primary response to a foreign antigen was considered unlikely because by using our culture conditions we could not obtain a primary antigen response or a secondary antigen response after in vitro priming to a variety of potent foreign antigens. Finally, the possibility that the syngeneic MLR represents a response to a variety of minor histocompatibility self antigens in association with self Ia molecules was eliminated by showing that the secondary responses to H-2 compatible, non-H-2 different strain (A/J vs. B10.A and C3H, or BALB/c vs. B10.D2 and DBA/2) were comparable to the secondary responses to syngeneic stimulators. Thus, we conclude that the target antigens in the syngeneic MLR are solely determinants on self Ia molecules, although the functionally equivalent possibility of a single, nonpolymorphic, minor self antigen seen in association with self Ia molecules cannot be excluded.

T-lymphocyte-enriched murine peritoneal exudate cells. IV. Genetic control of cross-stimulation at the T-cell level.

Antibodies raised against many structurally related antigens have been shown to cross-react extensively. Manifestations of T-cell immunity, on the other hand, appear to be more restricted in their ability to be elicited by cross-reacting antigens, although examples have been reported. This paper explores the nature of the cross-reactions at the T-cell level among the branched-chain copolymers (T,G)-A--L, (phi,G)-A--L, (H,G)-A--L, and G-A--L, as well as a related linear terpolymer, GAT, in a variety of mouse strains using the peritoneal exudate T-lymphocyte-enriched cells (PETLES) proliferation assay. (T,G)-A--L, (phi,G)-A--L, and GAT could cross-stimulate cells immune to the other two antigens, whereas (H,G)-A--L, (T,G)-Pro--L, and G-A--L showed no cross-stimulations. The extent of the cross-reactions varied with the mouse strain and was shown to be under the control of immune response genes. It was necessary for the strain to be able to respond to both the immunogen and the cross-reacting antigen, when used as an immunogen, in order for cross-stimulation to occur; however, this was not always sufficient. Several examples of unequal or one-way cross-reactions were found. In addition, the immune responses to (H,G)-A--L and (phi,G)-A--L showed no cross-reactions with the other antigen even though their Ir genes were both mapped to the K region or I-A subregion. The problem of accounting for such fine specificity of T-cell recognition in lieu of the genetic evidence demonstrating only Ir gene control of the response is discussed.

Early genetic events in T cell development analyzed by in situ hybridization.

In situ hybridization was used to investigate the expression of T cell receptor (TCR) alpha, beta, and gamma mRNAs in developing fetal and adult precursor thymocytes. gamma transcription was observed at the earliest time tested (day 12), followed by beta 12 h later, and TCR alpha on day 16. The early beta transcripts appeared to be from unrearranged or incompletely rearranged (D-J-C) beta loci. V beta region transcription was first detectable on day 14 and transcription of different V beta genes was induced at different times. These results delineate a schedule sequence of TCR gene activation, which begins within 1 d after entry of stem cells into the fetal thymus.

Activation events during thymic selection.

During their differentiation in the mouse thymus, CD4+8- cells undergo several of the sequential changes observed upon normal activation of mature, peripheral CD4+ lymphocytes. Expression of CD69, an early activation marker, is first observed on a minority of cells at the T cell receptor (TCR)lo/med double-positive stage, is maximal (50-90%) on heat-stable antigen (HSA)hi TCRhi double-positive, HSAhi TCRmed CD4+8lo, and HSAhi TCRhi CD4+8- cells, and is downmodulated at the mature HSAlo CD4+8- stage. In contrast, CD44, a late activation marker, is selectively expressed at the HSAlo stage. The set of lymphokines that CD4+8- thymocytes can produce upon stimulation also characteristically expands from mainly interleukin 2 (IL-2) at the HSAhi stage, to IL-2 and very large amounts of IL-4, IL-5, IL-10, and interferon gamma (IFN-gamma) at the HSAlo stage. 1 in 30 HSAlo CD4+8- adult thymocytes secrete IL-4 upon stimulation through their TCR. This frequency is 25% of the frequency of IL-2 producers, about 100-fold above that of peripheral (mainly resting) CD4+ T cells. With time after their generation in organ culture, CD4+8- thymocytes lose their capacity to secrete IL-4, IL-5, and IFN-gamma, but not IL-2. Similarly, the frequency of IL-4, but not of IL-2, producers progressively decreases after emigration to the periphery as judged by direct comparison between thymic and splenic CD4+ cells in newborns, or by following the fate of intrathymically labeled CD4+8- cells in adults after their migration to the spleen. This sequence suggests that thymic selection results from an activation process rather than a simple rescue from death at the double-positive stage, and shows that the functional changes induced after intrathymic activation, although transient, are still evident after export to the periphery.

Antigen presentation by resting B cells. Radiosensitivity of the antigen-presentation function and two distinct pathways of T cell activation.

In this report we have examined the ability of small resting B cells to act as antigen-presenting cells (APC) to antigen-specific MHC-restricted T cells as assessed by either T cell proliferation or T cell-dependent B cell stimulation. We found that 10 of 14 in vitro antigen-specific MHC-restricted T cell clones and lines and three of four T cell hybridomas could be induced to either proliferate or secrete IL-2 in the presence of lightly irradiated (1,000 rads) purified B cells and the appropriate foreign antigen. All T cell lines and hybridomas were stimulated to proliferate or make IL-2 by macrophage- and dendritic cell-enriched populations and all T cells tested except one hybridoma caused B cell activation when stimulated with B cells as APC. Furthermore, lightly irradiated, highly purified syngeneic B cells were as potent a source of APC for inducing B cell activation as were low density dendritic and macrophage-enriched cells. Lymph node T cells freshly taken from antigen-primed animals were also found to proliferate when cultured with purified B cells and the appropriate antigen. Thus, small resting B cells can function as APC to a variety of T cells. This APC function was easily measured when the cells were irradiated with 1,000 rads, but was greatly diminished or absent when they were irradiated with 3,300 rads. Thus, the failure of some other laboratories to observe this phenomenon may be the result of the relative radiosensitivity of the antigen-presenting function of the B cells. In addition, this radiosensitivity allowed us to easily distinguish B cell antigen presentation from presentation by the dendritic cell and macrophage, as the latter was resistant to 3,300 rads. Finally, one T cell clone that failed to proliferate when B cells were used as APC was able to recruit allogeneic B cells to proliferate in the presence of syngeneic B cells and the appropriate antigen. This result suggests that there are at least two distinct pathways of activation in T cells, one that leads to T cell proliferation and one that leads to the secretion of B cell recruitment factor(s).

Polyclonal stimulation of resting B lymphocytes by antigen-specific T lymphocytes.

Resting B lymphocytes are activated, proliferate, and differentiate into antibody-secreting cells when cultured with long-term lines of major histocompatibility complex (MHC)-restricted, antigen-specific T cell in the presence of the antigen for which the T cells are specific. Under optimal conditions, essentially all B cells are activated and approximately 35% enter S phase in the absence of antigens for which the B cells are specific. Activation and proliferation are observed in cells from both normal mice and mice with the xid-determined immune defect. Highly purified B cells bearing Ia molecules for which the T cells are "cospecific" can present antigen to T cells with the resulting T cell stimulation leading to the activation and proliferation of the antigen-presenting B cells. However, B cells that do not bear Ia molecules for which the T cells are cospecific are also activated and proliferate if antigen and a source of antigen-presenting B cells or macrophage-rich cells of proper histocompatibility type are present. Thus, resting B cells, both normal and "xid", can be activated by non-MHC restricted factors without receptor cross-linkage. Experiments are presented that support the concept that local production and action of such unrestricted activating factors may be responsible for the MHC-restriction of T cell-B cell interaction seen in many circumstances.

Antigen-specific T cell clones restricted to unique F1 major histocompatibility complex determinants. Inhibition of proliferation with monoclonal anti-Ia antibody.

The existence of T cells specific for soluble antigens in association with unique F(1) or recombinant major histocompatibility complex (MHC) gene products was first postulated from studies on the proliferative response of whole T cell populations to the antigen poly(Glu(55)Lys(36)Phe(9))(n) (GLphi). In this paper we use the newly developed technology of T lymphocyte cloning to establish unequivocally the existence of such cells specific for GLphi and to generalize their existence by showing that F(1)- specific cells can be isolated from T cell populations primed to poly(Glu(60)Ala(30)Tyr(10))(n) (GAT) where such clones represent only a minor subpopulation of cells. Gl.4b-primed B10.A(5R) and GAT-primed (B10.A x B10)F(1) lymph node T cells were cloned in soft agar, and the colonies that developed were picked and expanded in liquid culture. The GLphi-specific T cells were then recloned under conditions of high-plating efficiency to ensure that the final colonies originated from single cells. T cells from such rigorously cloned populations responded to stimulation with GILphi but only in the presence of nonimmune, irradiated spleen cells bearing (B10.A x B10)F(1) or the syngeneic B 10.A(5R) recombinant MHC haplotype. Spleen cells from either the B10 or B 10.A parental strains failed to support a proliferative response, even when added together. (B10 x B10.D2)F(1) and (B10 x B10.RIII)F(1) spleen cells also supported a proliferative response but (B10 x B10.Q)F(1) and (B10 X B10.S)F(1) spleen cells did not. These results suggested that the T cell clones were specific for GL[phi} in association with the beta(AE)(b)-alpha(E) (k,d,r,) Ia molecule and that recognition required both gene products to be expressed in the same antigen-presenting cells. Support for this interpretation was obtained from inhibition experiments using the monoclonal antibody Y-17 specific for a determinant on the beta(AE)(b)-alphaE Ia molecule. Y-17 completely inhibited the proliferative response of a GLphi-specific clone but had no effect on the response of either a PPD-specific or GAT-specific clone, both of which required the beta(A)-alpha(A) Ia molecule as their restriction element. No evidence could be found for the involvement of suppressor T cells in this inhibition. We therefore conclude that the phenomenon of F(1)-restricted recognition by proliferating T cells results from the presence of antigen- specific clones that must recognize unique F(1) or recombinant Ia molecules on the surface of antigen-presenting cells in addition to antigen in order to be stimulated.

Immune response gene function correlates with the expression of an Ia antigen. I. Preferential association of certain Ae and E alpha chains results in a quantitative deficiency in expression of an Ae:E alpha complex.

These studies were stimulated by the observation, reported in the accompanying paper (19), that IEu failed to interact with I-Ak or I-As in F1 mice to allow a response to the antigen, pigeon cytochrome c, unlike I-E subregions derived from other Ia.7+ haplotypes. Serological and biochemical analyses were performed to determine whether or not cells from these F1 mice express the Ak,se:E alpha complexes that should function as restriction elements for T cell recognition of pigeon cytochrome c on antigen-presenting cells. Using the Y-17 monoclonal antibody, which recognizes the combinatorial or conformational determinant Ia.m44 on certain Ae:E alpha complexes, we were able to distinguish between Aue:Eu alpha and Ab,k,se:Eu alpha complexes on cell surfaces. Although complement-dependent microcytotoxicity with Y-17 failed to detect Ab,k,se:Eu alpha complexes on cells from appropriate F1 mice, these molecules were detected by both quantitative absorption and quantitative immunofluorescence studies. However, Ab,k,se:Eu alpha complexes were found to be present at levels only one-seventh to one-eighth the levels expressed by homozygous I-Ab, I-Ek; I-Ak, I-Ek; and I-As, I-Ek cells. The results of two-dimensional polyacrylamide gel electrophoresis analyses suggest that the low levels of expression of Ab,k,se:Eu alpha complexes are a consequence of the preferential association of Aue and Eu alpha chains with each other in the F1 cells. As will be shown in the following paper (19), the quantitative deficiency in the expression of Ake:Eu alpha and Ase:Eu alpha complexes results in a corresponding defect in antigen-presenting cell function, thus providing strong evidence that Ia antigens represent products of Ir genes.

Monoclonal antibody against an Ir gene product?

Genetic, biochemical, and functional studies have been performed using a monoclonal antibody, Y-17, directed at a conformational or combinatorial determinant formed by certain Ae:E alpha complexes. This determinant appears to be a marker present on a subset of B cells as well as on non-T and non-B spleen cells. Besides Ae and E alpha chains, Y-17 precipitates a third chain that is indistinguishable from the A alpha chain in two-dimensional gels. This results suggests additional combinatorial complexity in the generation of I-region encoded antigens. Y-17 can inhibit the response of T cells to Ae:E alpha determinants in mixed lymphocyte cultures. Furthermore, Y-17 blocks antigen-specific T cell proliferative responses to GLPhe and pigeon cytochrome c which have been shown to require the Ae:E alpha complex as a restriction element for antigen presentation. These results provide strong evidence for the molecular identity of Ia antigens, Ir-gene products and Lad antigens.

Contribution of antigen-presenting cell major histocompatibility complex gene products to the specificity of antigen-induced T cell activation.

Previous studies from our laboratory showed that B 10.A mice are high responders to pigeon cytochrome c fragment 81-104, whereas'B 10.A(5R) mice are low responders. In the present studies, the C-terminal cyanogen bromide cleavage fragment and homologous synthetic peptides of tobacco horn worm moth cytochrome c were shown to be immunogenic in both B10.A and B10.A(5R) mice. These strains, however, showed different patterns of cross-reactivity when immune lymph node T cells were stimulated with cytochrome c fragments from other species. To examine the two patterns of responsiveness at a clonal level, cytochrome c fragment-specific T cell hybridomas were made and found to secrete interleukin 2 in response to antigen. The patterns of cross- reactivity of these B 10.A and B 10.A(5R) clones were similar to that seen in the whole lymph node population. Surprisingly, when these clones were tested for major histocompatibility complex (MHC)-restricted antigen recognition, they were all found to respond to antigen with both B10.A and B10.A(5R) antigen-presenting cells (APC). Furthermore, the cross-reactivity pattern appeared to be largely determined by the genotype of the APC, not the genotype of the T cell clone. That is, a given T cell clone displayed a different fine specificity when assayed with B10.A or B10.A(5R) APC. This observation indicates that the APC MHC gene product and antigen interact during the stimulation of the T cell response and that as a consequence the specificity of antigen-induced T cell activation is influenced by these MHC gene products. (During the preparation of this manuscript it has come to our attention that results similar to our own, concerning the fine specificity of cytotoxic T cell clones, have been obtained by Dr. T. R. Hunig and Dr. M. J. Bevan, Massachusetts Institute of Technology, Boston, MA. T. R. Hunig and M. J. Bevan. 1981. Specificity of T-cell clones illustrates altered self hypothesis. Nature. 294:460.)

T and B cells that recognize the same antigen do not transcribe similar heavy chain variable region gene segments.

We have attempted to determine whether T cells and B cells that have the same antigenic specificity and whose receptors share idiotypic determinants in fact express similar VH gene segments. To do this, we have obtained and characterized a cDNA clone containing the entire coding sequence for the VH gene from a glutamic acid60/alanine30/tyrosine10 (GAT)-binding immunoglobulin that carries the CGAT idiotype. The GAT-VH clone was hybridized to Northern blots of GAT-specific T cell RNAs; there was no evidence of a T cell transcript that hybridized to the GAT-VH probe. The T cells analyzed included: (a) 10 GAT-binding suppressor T cell hybridomas, 6 of which secreted factors with CGAT idiotypic determinants, (b) one GAT-specific helper T cell hybridoma, and (c) two GAT-specific helper T cell lines grown in the absence of feeder cells. The detection limit of the Northern blot analysis was 1-2 copies of a particular mRNA species per cell for the hybridomas and 5-10 copies per cell for the T cell lines. Therefore, we conclude that T and B lymphocytes responding to GAT do not utilize similar VH gene segments. Furthermore, the presence of idiotypic determinants on T lymphocytes does not necessarily imply close structural similarity between T and B cell antigen receptors.