Ia Restriction Specificity of KLH-Specific T Cells from Allogeneic Bone Marrow Chimeras Is Influenced by Histocompatibility at the H-2 and Minor Histocompatibility Loci

Ia restriction specificity involved in T cell proliferative responses to keyhole limpet hemocyanin (KLH) has been analyzed using a variety of allogeneic bone marrow chimeras. The chimeric mice were prepared by reconstituting irradiated AKR, SJL, B10.BR and B10.A(4R) mice with bone marrow cells from B10 mice. When such chimeric mice had first been primed with KLH in complete Freund's adjuvant (CFA), T cells from H-2 incompatible fully allogeneic chimeras showed significantly higher responses to KLH in the presence of antigen-presenting cells (APC) of donor strain (B10) than APC of recipient strain. However, in H-2 subregion compatible chimeras, [B10→B10.A(4R)], which were matched at the H-2D locus and at minor histocompatible loci, the T cells could mount vigorous responses to KLH with antigen-presenting cells (APC) of either donor or recipient type. The same results were obtained as well with chimeras that had been thymectomized after full reconstitution of lymphoid tissues by donor-derived cells. A considerable proportion of KLH-specific T cell hybridomas established from [B10→B10.A(4R)] chimeras exhibited both I-A^b and I-A^k restriction specificities. The present findings indicate that the bias to donor Ia type of antigen specific T cells is determined by donor-derived APC present in the extrathymic environment but that cross-reactivity to the recipient Ia is influenced to some degree by histocompatibility between donor and recipient mice, even though the histocompatible H-2D locus and minor histocompatibility loci seem not to be directly involved in the I-A restricted responses studied herein.     

Functionally distinct agretopic and epitopic sites. Analysis of the dominant T cell determinant of moth and pigeon cytochromes c with the use of synthetic peptide antigens

The dominant T cell determinant on moth and pigeon cytochromes c in B10.A (E beta k:E alpha k) mice is located in the C-terminal portion of the protein, contained within residues 93-103 or 93-104. Thirty-seven antigen analogs, containing single amino acid substitutions at positions 98, 99, 101, 102, 103, and 104, were synthesized. The effects of the substitutions on in vitro antigenicity and in vivo immunogenicity were determined. Functional assays with T cell clones identified residues 99, 101, 102, and 103 as critical, based on their effect on antigenic potency. Peptides containing substitutions at residues 99, 101, and 102 were capable of eliciting unique clones upon immunization of B10.A mice. This was consistent with the identification of these residues as part of the epitope, the site on the antigen that interacts with the T cell receptor. Immunization with peptides substituted at residue 103, however, failed to elicit clones with unique specificity for the immunogen. When these peptides were tested for their ability to stimulate the T cell clones with antigen-presenting cells from B10.A(5R) mice expressing the E beta b:E alpha k Ia molecule, a consistent change in the relative antigenic potency was observed with 50% of the peptides. The effect of the Ia molecule on the antigenic potency ruled out the possibility that residue 103 nonspecifically affected antigen uptake or processing and identified residue 103 as part of the agretope, the site that interacts with the Ia molecule. The locations of the agretope and the epitope on this antigenic determinant appear to be fixed, even in the presence of large numbers of amino acid substitutions. However, some substitutions were found to affect both the agretope and the epitope, placing limits on the functional independence of the two sites. The results are discussed in terms of the trimolecular complex model of T cell activation and the implications of these data for antigen-Ia molecule interactions.     

Two distinct mechanisms account for the immune response (Ir) gene control of the T cell response to pigeon cytochrome c

Previous experiments have demonstrated that the immune response of MHC congenic mice to pigeon cytochrome c is under Ir gene control. Expression of I-E-encoded gene products influences both the magnitude and fine specificity of the Th cell response to pigeon cytochrome c and phylogenetic derivatives. Results of those experiments implicate both determinant selection and repertoire selection as mechanisms of Ir gene control in this system. In this report we have compared the TCR expressed in pigeon cytochrome c-reactive Th cells from B10.A(I-Ek), B10.A(5R) (I-Eb), and B10.S(9R) (I-Es) mice. The B10.A(5R) strain is a low responder to pigeon cytochrome c, but in response to moth cytochrome c this strain produces T cells which respond to pigeon or moth cytochrome c on B10.A APC. These cells are phenotypically identical to the predominant clonal phenotype seen in the B10.A response to pigeon cytochrome c. In this report, we show that the B10.A and B10.A(5R) pigeon cytochrome c-reactive T cells express essentially identical T cell receptors. These results, coupled with recent studies reporting a relatively low affinity for I-Eb molecules by pigeon cytochrome c peptides compared with moth cytochrome c peptides, strongly argue that the immune response defect in the B10.A(5R) strain is due to a defect in Ag presentation (determinant selection). In contrast, B10.A and B10.S(9R) strains are high responders to pigeon cytochrome c. Both strains produce T cell clones which are capable of responding to cytochrome c presented by either B10.A or B10.S(9R) APC in vitro. We show that, even in T cells with this MHC restriction degeneracy, the TCR expressed in the two strains are different. Because the APC of both strains can clearly present the cytochrome c Ag, we conclude that the differential expression of the TCR in the responses is due to a T cell repertoire selection difference in the two strains. Thus, for the response to one Ag in three MHC congenic strains, there exists evidence that both determinant selection and repertoire selection can be mechanisms of Ir gene control of an immune response.     

The fine specificity of antigen and Ia determinant recognition by T cell hybridoma clones specific for pigeon cytochrome c

The activation of proliferative T lymphocytes normally involves the simultaneous recognition of a particular foreign antigen and a particular Ia molecule on the surface of antigen-presenting cells, the phenomenon of major histocompatibility complex (MHC) restriction. An analysis of T cell clones specific for pigeon cytochrome c, from B10.A and B10.S(9R) strains of mice, revealed the unusual finding that several of the clones could respond to antigen in association with Ia molecules from either strain. Using these cross-reactive clones, we performed experiments which demonstrated that both the Ia molecule and the T cell receptor contribute to the specificity of antigen recognition; however, MHC-linked low responsiveness to tuna cytochrome c (an immune response gene defect) could not be attributed solely to the efficacy with which the Ia molecules associated with the antigen. These results imply that antigen and Ia molecules are not recognized independently, but must interact at least during the process of T cell activation.     

H-2-linked Ir gene control of T cell recognition of the Sm nuclear autoantigen and the aberrant response of autoimmune MRL/Mp-+/+ mice

We have examined T cell recognition of the nuclear autoantigen Sm. Rabbit Sm-primed cells from autoimmune MRL/Mp-+/+ (+/+) mice and from all normal strains tested were able to proliferate to rabbit Sm in vitro. In contrast, the reactivity of normal strains to Sm of murine origin was genetically restricted; only H-2f strains B10.M and A.CA, and H-2s strains B10.S and A.SW could recognize mouse Sm, suggesting that responsiveness to mouse Sm was under the control of H-2-linked Ir genes. Although five Iak-bearing normal strains (B10.A, B10.A(2R), B10.BR, A/Sn, and CBA) did not recognize mouse Sm, autoimmune +/+ (Iak) mice were responders. The responsiveness of the +/+ mice to Sm was probably not due to differences in their Iak region, compared with other strains, because the Iak region of normal strains and the autoimmune +/+ strain were indistinguishable by interstrain MLC, immune response gene product function, and recognition by anti-Iak mAb. Inhibition of Sm-induced proliferation by mAb demonstrated that T cells from autoimmune +/+ mice, responder normal strains, and nonresponder normal strains recognized rabbit and mouse Sm in the context of I region-encoded products. The T cell response to Sm antigen in normal mice is therefore Ia region restricted and, for the murine antigen, under Ir gene control. Autoimmune mice that spontaneously make anti-Sm antibodies (+/+) also perceive Sm in an Ia-restricted manner, but their responder status abrogates H-2-linked Ir gene control.     

Identification of distinct predominant epitopes recognized by myoglobin-specific T cells under the control of different Ir genes and characterization of representative T cell clones

We characterized the fine specificity of antigen recognition of myoglobin-immune T cells from B10.D2, B10.GD, and B10.A(5R) mice. Polyclonal H-2d T cells show a predominant response to an epitope centering on Glu 109 and His 116. These residues localize a dominant epitope to one segment of the myoglobin surface, but probably are not the only amino acid residues involved. This response pattern maps genetically to I-Ad (or Kd) based on the B10.GD recombinant strain. A different epitope specificity was detected in B10.A(5R) T cells mapping to I-E beta b E alpha k or I-Cd, but no difference was detected between strains differing at the Igh locus. Thus, epitope specificity varied with Ia haplotype but not Igh allotype. Myoglobin-specific B10.D2 T cell lines were established, and five clones specific for the Glu 109, His 116 epitope were isolated; these were all restricted to I-Ad antigen-presenting cells. These clones represent the dominant specificity in the polyclonal T cell response to myoglobin and will be useful in characterizing the structure and function of T cell receptors for antigen and Ia. The differences in number and nature of T cell epitopes compared to B cell epitopes of myoglobin are discussed.     

Fine specificity of antigen recognition by T cell hybridoma clones specific for poly-18: a synthetic polypeptide antigen of defined sequence and conformation

Antigen-specific T cell blasts to poly-18, a polypeptide antigen of defined sequence and conformation, were generated from lymph nodes of antigen-primed BALB/cCr mice. These blasts were fused with the BW5147 thymoma to obtain anti-poly-18-reactive T cell hybridomas. All of the hybridomas were IAd-restricted and secreted IL2 in the presence of IAd/poly-18. On the basis of fine specificity analysis, these hybridomas were classified into two groups. Group A hybridomas recognized a minimal peptide sequence of Glu-Tyr-Lys-(Glu-Tyr-Ala)3-Glu-Tyr-Lys, whereas Group B needed the sequence Glu-Tyr-Ala-(Glu-Tyr-Ala)3-Glu-Tyr-Lys/Ala for activation. Three critical residues were identified in Group A hybridomas: the alanine residue at position 9, the carboxy terminal lysine, and the lysine at position 3. In Group B hybridomas, the alanine at position 3 was found to be the critical residue. We suggest that the amino acid residue at position 3 (lysine/alanine) is the T cell receptor contact residue on the poly-18 antigen in BALB/cCr mice.     

Antigen presentation by human antigen-presenting cells to antigen-specific xenogeneic murine T cells

Successful antigen presentation by xenogeneic human antigen-presenting cells (APC) to stimulate the proliferation of antigen-specific, keyhole limpet hemocyanin (KLH)-specific, ovalbumin (OVA)-specific, and purified protein derivative of Mycobacterium tuberculosis (PPD)-specific murine T cells was observed. Evidence indicating a direct cell interaction between antigen-specific murine T cells and xenogeneic human APC was given by experiments using antigen-specific murine T cell clones. The OVA-specific B10.S(9R) T cell line (9-0-A1) and PPD-specific B10.A(4R) T cell line (4-P-1) were stimulated by both xenogeneic human APC and murine APC from syngeneic or I-A compatible strains, while the PPD-specific human T cell line (Y-P-5) was stimulated by autologous human APC but not by murine APC. Anti-HLA-DR monoclonal antibodies (MoAb) blocked the xenogeneic human APC-antigen-specific murine T cell clone interaction. Thus, human xenogeneic APC can stimulate antigen-specific murine T cells through HLA-DR molecules in the same manner as syngeneic murine APC do through Ia molecules coded for by the I region of the H-2 complex, while murine APC failed to present antigen to stimulate human antigen-specific T cells.     

Major histocompatibility complex-linked control of the murine immune response to myelin basic protein

Recent experiments have shown that different regions of myelin basic protein (MBP) are encephalitogenic for different inbred strains of mice. It was therefore of interest to determine whether the immune response to MBP was MHC associated, and if so, what subregion controlled this response. Because PL/J and A/J mice were good responders to mouse MBP and C57Bl/10SN were not, B10.PL(73NS) and B10.A mice were immunized with mouse MBP under conditions designed to induce EAE. These strains were found to be highly susceptible. Intra-H-2 recombinant mice were then assessed for susceptibility. B10.A(4R) and B10.MBR were susceptible, whereas B10.A(5R) were resistant. Thus, EAE induced by purified MBP is under the control of the MHC, and the response maps to the I-A subregion. Production of IL 2 in vitro by T cells from MBP-primed mice in the presence of antigen and adherent cells was blocked by monoclonal antibody to the I-A, but not the I-E, subregion. When the specificity of the encephalitogenic response was tested, peptide 1-37 was active in B10.PL(73NS) and B10.A mice, whereas peptide 89-169 was active in A.SW, SWR, and B10.T(6R) strains. Serum from mice immunized with MBP peptides was assayed for antibody content. PL, B10.PL, and B10.A mice made a good antibody response to peptides 1-37 and 43-88 but were nonresponsive to peptide 89-169. SJL, A.SW, SWR, and B10.T(6R) mice responded well to peptide 89-169 but were poorly responsive to peptides 1-37 and 43-88.     

Unusually diverse T cell response to a repeating tripeptide epitope.

The immune system utilizes a diverse T cell repertoire for the recognition of foreign antigens in the context of self MHC gene products. We have examined the potential diversity of the T cell response directed to a immunodominant repeating tripeptide epitope (EYA)5. This peptide represents one of the two T cell epitopes on the synthetic alpha-helical polypeptide antigen Poly 18, Poly EYK(EYA)5 in H-2d mice and does not require antigen processing prior to presentation to Poly 18-specific T cell hybridomas. The T cell response directed to the repeating tripeptide epitope (EYA)5 is extremely heterogenous even though the epitope has a relatively simple amino acid sequence. We have analyzed the fine specificity of 21 randomly chosen Poly 18-reactive, (EYA)5-specific and H-2d-restricted T cell hybridomas derived from H-2d, H-2bxd, and H-2b----H-2bxd Poly 18-responding mice to determine the number of unique antigen reactivity patterns represented by this T cell population. We used alanine- and/or lysine-substituted (EYA)5 peptides and a panel of haplotype-varied splenocytes and observed a great deal of microheterogeneity in response. We find that 13 of the 21 hybridomas have a distinct fine antigen specificity and T cell receptors. The binding of (EYA)5 to the antigen-binding groove of I-Ad appears to generate a highly diversified T cell response. Therefore, (EYA)5-I-Ad complex allows the activation of unrelated T cell clonotypes with the same overall antigen specificity and MHC restriction, but with distinct microheterogeneity in response and receptor usage.     

Antigen presentation by hapten-specific B lymphocytes. II. Specificity and properties of antigen-presenting B lymphocytes, and function of immunoglobulin receptors

The studies described in this paper were designed to examine the ability of hapten-binding murine B lymphocytes to present hapten-protein conjugates to protein antigen-specific, Ia-restricted T cell hybridomas. BALB/c B cells specific for TNP or FITC presented hapten-modified proteins (TNP-G1 phi, TNP-OVA, or FITC-OVA) to the relevant T cell hybridomas at concentrations below 0.1 microgram/ml. Effective presentation of the same antigens by B lymphocyte-depleted splenocytes, and of unmodified proteins by either hapten-binding B cells or Ig spleen cells, required about 10(3)-to 10(4)-fold higher concentrations of antigen. The use of two different haptens and two carrier proteins showed that this extremely efficient presentation of antigen was highly specific, with hapten specificity being a property of the B cells and carrier specificity of the responding T cells. The presentation of hapten-proteins by hapten-binding B lymphocytes was radiosensitive and was not affected by the depletion of plastic-adherent cells, suggesting that conventional APCs (macrophages or dendritic cells) are not required in this phenomenon. Antigen-pulsing and antibody-blocking experiments showed that this hapten-specific antigen presentation required initial binding of antigen to surface Ig receptors. Moreover, linked recognition of hapten and carrier determinants was required, but these recognition events could be temporally separated. Finally, an antigen-processing step was found to be necessary, and this step was disrupted by ionizing radiation. These data suggest a role for B cell surface Ig in providing a specific high-affinity receptor to allow efficient uptake or focusing of antigen for its subsequent processing and presentation to T lymphocytes.     

The T cell receptor V beta 6 domain imparts reactivity to the Mls-1a antigen

A monoclonal antibody secreting hybridoma was established by fusing spleen cells from a rat immunized with a murine T cell clone, OI11, which has I-Ab restricted specificity for the male H-Y antigen and unrestricted specificity for the minor lymphocyte stimulating antigen, Mls-1a, to the mouse myeloma P3X63AG8.653 and screening for the capacity of the hybridoma supernatants to stimulate the OI11 T cell clone. An antibody (RR4-7) was found to be specific not only for the immunizing T cell clone but virtually for all T cells using the V beta 6 TCR gene product as part of their surface antigen receptor. When the expression of the V beta 6 gene in various strains of mice was analyzed, it was found that strains expressing the Mls-1a antigen contained few T cells expressing V beta 6-encoded TCRs. The majority of T cell hybridomas which expressed V beta 6-encoded TCRs were found to be reactive to the Mls-1a antigen. These data confirm the finding of H. R. MacDonald et al. (Nature (London) 332, 40, 1988) that most TCRs encoded by the V beta 6 gene have a biased specificity for the Mls-1a antigen.     

T cell-mediated recognition of foreign antigen and the Ia molecule observed by stopped-flow fluorometry

Th cell-mediated rapid recognition of foreign Ag and the Ia molecule was studied using azobenzenearsonate-L-tyrosine (ABA-L-tyrosine)-specific Th cells (I-Ak restricted), foreign Ag (ABA-L-tyrosine), and APC (H-2k). Initial transmembrane signals in Th cell hybridomas (2-45-12) and in Th cell lines (A24-17 or A33-7) were monitored by stopped-flow fluorometry with fluorescent probes. It was found that Th cells recognized foreign Ag within 1 s at 25 degrees C on the APC (B10.BR spleen cells or L cells into which I-Ak genes were transferred). Recognition of foreign Ag and the Ia molecule was shown to deliver the initial signals to Th cell hybridomas and T cell lines. First, Th cells had membrane fluidity increased and then calcium was transported from the external medium into the T cells. The initial transmembrane signals to Th cell hybridomas were inhibited by the addition of an anti-I-Ak mAb. None of the initial signals were observed in the absence of either specific foreign Ag or APC.     

The pigeon cytochrome c-specific T cell response of low responder mice. I. Identification of antigenic determinants on fragment 1 to 65

An examination of the proliferative response to pigeon cytochrome c fragments 1 to 65 and 1 to 80 by T cells from mice that are low responders to the native molecule revealed that some of the strains could respond to antigenic determinants on these fragments. T cell clones derived from B10.A(3R) and B10.A(4R) mice were used to characterize the antigenic determinants on fragment 1 to 65. All of the clones recognized syngeneic A beta:A alpha Ia molecules as their restriction element. Three B10.A(3R) clones and six B10.A(4R) clones recognized fragment 39 to 65. Another four B10.A(4R) clones responded to fragment 1 to 38. By stimulating with a series of cytochrome c fragments from different species, as well as a synthetic peptide, it was possible to localize the antigenic determinant(s) recognized by the B10.A(3R) clones to residues 45 to 58. Each clone showed a unique pattern of responsiveness to the various fragments, suggesting a diversity of T cell receptors specific for the same peptide. One B10.A(3R) clone could be stimulated by many of the 1 to 65 fragments in association with allogeneic B10.SM presenting cells and by tuna fragment 1 to 65 in association with B10.M presenting cells, although the rank order of potency for several of the fragments was different than that observed with syngeneic antigen-presenting cells. In addition, the clone was poorly reactive to a synthetic peptide containing a conservative substitution, serine for threonine, at position 49. The implications of these results for subsite dissection (agretope and epitope) of the antigenic determinant recognized by this clone are discussed.     

Immunity to leprosy. II. Genetic control of murine T cell proliferative responses to Mycobacterium leprae

T cell proliferative responses to Mycobacterium leprae were measured after immunization of mice at the base of the tail with antigen and challenging lymphocytes from draining lymph nodes in culture with M. leprae. This T cell response to M. leprae has been compared in 18 inbred strains of mice. C57BL/10J mice were identified as low responder mice. The congenic strains B10.M and B10.Q were found to be high responders, whereas B10.BR and B10.P were low responders. F1 (B10.M X C57BL/10J) and F1 (B10.Q X C57BL/10J) hybrid mice were found to be low responders, similar to the C57BL/10J parent, indicating that the low responsive trait is dominant. Whereas B10.BR mice were shown to be low responders to M. leprae, B10.AKM and B10.A(2R) were clearly high responders, indicating that the H-2D region influences the magnitude of the T cell proliferative response. Gene complementation within the H-2 region was evident. Genes outside the H-2 region were also shown to influence the response to M. leprae. C3H/HeN were shown to be high responder mice, whereas other H-2k strains, BALB.K, CBA/N, and B10.BR, were low responders. Gene loci that influence the T cell proliferation assay have been discussed and were compared to known background genes which may be important for the growth of intracellular parasites. Because mycobacteria are intracellular parasites for antigen-presenting cells, genes that affect bacterial growth in these cells will also influence subsequent immune responses of the host.     

Genetic regulation of the antibody response to H-2Db alloantigens in mice. IV. Antigens that activate helper T cells for IgG, coded for by the non-H-2 genome

When B10.A(5R) mice are immunized with congenic C57BL/10 cells only 2-ME-sensitive antibodies (IgM type) are found directed against H-2Db. To obtain 2-ME-resistant antibodies (IgG type) 5R mice must be immunized with noncongenic cells (e.g., A.BY); in this case non-H-2 cell surface antigens will activate helper T cells to induce anti-Db IgG antibody production by B cells. An attempt was made to define helper antigens that activate helper T cells. Neither N-2 antigens of seven H-2Db recombinant strains nor a limited set of non-H-2 cell surface antigens were able to serve as helper antigens. By using individual backcross mice as antigen, one helper antigen was found on the background of strain A under the conditions used, whereas other backgrounds may carry more than one antigen. The helper antigen is dominantly expressed in F1 mice and has to be presented on the same cell as H-2Db to induce the switch from IgM to IgG.     

Contribution of antigen processing to the recognition of a synthetic peptide antigen by specific T cell hybridomas

Most antigens recognized by T cells require unfolding or partial degradation (processing) followed by association with Major Histocompatibility Complex (MHC) molecules. We examined the processing requirements for the presentation of antigen to two T cell hybridomas which recognize the alpha-helical synthetic polypeptide antigen Poly 18, Poly [EYK(EYA)5], in association with I-Ad. Hybridoma A.1.1 responds to EYK(EYA)4 as the minimum antigenic sequence while hybridoma B.1.1 recognizes (EYA)5 sequence. It was found that these hybridomas responded to Poly 18 and to minimum peptide sequences presented by glutaraldehyde and chloroquine treated antigen presenting cells (APC), suggesting that antigen processing is not a requirement for the activation of these cells. The reactivity pattern of hybridoma B.1.1 in the presence of glutaraldehyde fixed APC revealed that antigens containing lysine were presented with much less efficiency than antigens without lysine, suggesting an interaction of these residues with the antigen presenting cell surface. We discuss the possibility that alanine residues in the alpha-helical Poly 18 form a hydrophobic ridge which may be required for appropriate interaction between antigen, the T cell receptor, and MHC molecules.     

In vivo and in vitro regulation of IgE production in murine hybridomas

Normal BALB/c mice injected i.p. with the IgE-secreting hybridomas B53 (epsilon, kappa anti-DNP), SE1.3 (epsilon, kappa, anti-arsonate) or A3B1 (epsilon, kappa, anti-TNP) were monitored for serum IgE concentrations and frequencies of splenic T lymphocytes with surface membrane receptors for the Fc portion of IgE (Fc epsilon R+ T lymphocytes). Mice with B53 or SE1.3 hybridomas initially developed high concentrations of IgE and CD8+ Fc epsilon R+ T lymphocytes, followed by a progressive decline in both serum IgE and expression of cytoplasmic epsilon-chains in the hybridoma cells. Serum IgE concentrations in mice with A3B1 hybridomas progressively increased without development of Fc epsilon R+ T lymphocytes nor a subsequent decline in IgE or change in cytoplasmic epsilon-chain expression in the A3B1 cells. An in vitro system in which the IgE-secreting hybridoma cells were cocultured with spleen cells harvested from mice with established B53 tumors was used to investigate the mechanisms involved in the inhibition of IgE production by the hybridoma cells. The results of these studies indicate that: 1) the induction/upregulation of Fc epsilon R on CD8+ T lymphocytes in vivo requires factors in addition to high serum IgE concentrations; 2) in addition to CD8+ Fc epsilon R+ T lymphocytes and monocytes, another, as yet unidentified, splenic cell component appears to contribute to the process by which epsilon-chain expression in IgE-secreting hybridoma cells is suppressed, and 3) a hybridoma (A3B1) that fails to induce CD8+, Fc epsilon R+ T lymphocytes in vivo and is not inhibited in IgE expression in vivo, nonetheless is inhibited in IgE expression in vitro when cocultured with spleen cells from mice with B53 tumors.     

Cloned protein antigen-specific, Ia-restricted T cells with both helper and cytolytic activities: mechanisms of activation and killing

Myoglobin-specific, Iad-restricted cloned helper T cells and T hybridomas were found to directly kill Iad-bearing, myoglobin-pulsed B lymphoma targets and could also kill bystander targets, but only in the presence of antigen-pulsed antigen presenting cells (APC). The induction of the killing requires recognition of processed antigen in the context of class II major histocompatibility complex (MHC) molecules. Despite the specificity of induction, the bystander killing suggests a nonspecific lytic mechanism. The direct killing can be inhibited only by cold specific targets, whereas the bystander killing can be blocked by both specific and nonspecific targets. The cold target inhibition seems to be due to interference with effector-to-target contact or proximity rather than due to high-dose suppression of T-cell activation. Experiments using T-cell supernatants or cyclosporin A suggested that the helper T cells kill targets by synthesizing short-range soluble factor(s) with nonspecific killing activity de novo during the effector phase, but only while antigen-specific signal transduction is occurring. The mechanism of cold target inhibition appears to be absorption or consumption of a short-acting cytotoxic lymphokine by cells which must be able to interact closely with the effector cell. Normal spleen B cells, despite their capability for activating the helper T cells, cannot inhibit specific killing or be killed by helper T cells, even after lipopolysaccharide stimulation. Thus, although killing by helper T cells may play a negative feedback role in the normal immune response, our data raise the possibility that the helper T-cell-mediated killing may contribute to the immune surveillance against malignancy by virtue of the preferential killing of tumor cells either directly or indirectly.     

Genetic regulation of the immune response to hepatitis B surface antigen (HBsAg). V. T cell proliferative response and cellular interactions

We previously demonstrated that in vivo antibody production to HBsAg in the mouse is regulated by at least two immune response (Ir) genes mapping in the I-A (HBs-Ir-1) and I-C (HBs-Ir-2) subregions of the H-2 locus. To confirm that H-2-linked Ir genes regulate the immune response to HBsAg at the T cell level and to determine if the same Ir genes function in T cell activation as in B cell activation, the HBsAg-specific T cell responses of H-2 congenic and intra-H-2 recombinant strains were analyzed. HBsAg-specific T cell proliferation, IL 2 production, and the surface marker phenotype of the proliferating T cells were evaluated. Additionally, T cell-antigen-presenting cell (APC) interactions were examined with respect to genetic restriction and the role of Ia molecules in HBsAg presentation. The HBsAg-specific T cell proliferative responses of H-2 congenic and intra-H-2 recombinant strains generally paralleled in vivo anti-HBs production in terms of the Ir genes involved, the hierarchy of responses status among H-2 haplotypes, antigen specificity, and kinetics. However, the correlation was not absolute in that several strains capable of producing group-specific anti-HBs in vivo did not demonstrate a group-specific T cell proliferative response to HBsAg. The proliferative responses to subtype- and group-specific determinants of HBsAg were mediated by Thy-1+, Lyt-1+2- T cells, and a possible suppressive role for Lyt-1-2+ T cells was observed. In addition to T cell proliferation, HBsAg-specific T cell activation could be measured in terms of IL 2 production, because anti-HBs responder but not nonresponder HBs-Ag-primed T cells quantitatively produced Il 2 in vitro. Finally, the T cell proliferative response to HBsAg was APC dependent and genetically restricted in that responder but not nonresponder parental APC could reconstitute the T cell response of (responder X nonresponder)F1 mice, and Ia molecules encoded in both the I-A and I-E subregion are involved in HBsAg-presenting cell function.