Self-tolerance alters T-cell receptor expression in an antigen-specific MHC restricted immune response

Mls: A Link Between Immunology and Retrovirology

The nature of the mysterious minor lymphocyte stimulating (Mls) antigens has recently been clarified. These molecules which were key elements for our current understanding of immune tolerance, have a strong influence on the mouse immune system and are encoded by the open reading frame (orf) of endogenous and exogenous mouse mammary tumor viruses (MMTV's). The knowledge that these antigens are encoded by cancerogenic retroviruses opens an interdisciplinary approach for understanding the mechanisms of immune responses and immune tolerance, retroviral carcinogenesis, and retroviral strategies for infection.

Mouse endogenous superantigens: Ms and Mls-like determinants encoded by mouse retroviruses

Commonly used inbred mouse strains express different combinations of integrated mouse mammary tumor proviruses (MMTV). This appendix summarizes the proviruses that have been detected. The reported functional properties of those MMTV proviral products which have been identified as superantigens are also summarized, including the ability to elicit primary or secondary T cell responses and to induce Vb-specific clonal deletion during T cell differentiation. In addition, the amino acid sequences of putative ORF gene products of different MMTV are compared.

Antigen-Driven Selection of TCR In Vivo: Related TCR α-Chains Pair with Diverse TCR β-Chains

Ag-driven selection mediates effective T cell help and the development of Th cell memory in vivo. To analyze the dynamics of interclonal competition during the selection process in vivo, we use the I-Ek-restricted murine response to pigeon cytochrome c (PCC). The dominant PCC-specific clonotype expresses Vα11Vβ3 V regions with preferred sequence features in the third hypervariable regions (CDR3). In the current study we define and quantitatively monitor four subdominant PCC-specific clonotypes that express Vα11 paired with non-Vβ3 TCR β-chains (Vβ6, Vβ8.1/8.2, Vβ8.3, and Vβ14). The subdominant clonotypes emerge with similar dynamics to the dominant clonotype and together amount to similar numbers as the dominant clonotype in vivo. These subdominant clonotypes do not efficiently enter germinal centers, although they enter the memory compartment and rapidly re-emerge upon secondary challenge. Analysis of CDR3 diversity in the TCR α-chains identifies many preferred sequence features expressed by the dominant clonotype. These studies quantitatively demonstrate selection for diverse Th cells in vivo and highlight TCR α-chain dominance in Ag-driven selection for best fit.

Influence of the additional injection of host-type bone marrow on the immune tolerance of minor antigen-mismatched chimeras: possible involvement of double-negative (natural killer) T cells

BACKGROUND

It has previously been demonstrated that adding T cell-depleted (TCD) host bone marrow (BM) to an MHC-mismatched BM inoculum allows for induction of long-term stable chimeras without graft-versus-host disease (GVHD) even when non-TCD allogeneic BM was used.

AIMS

The present study was undertaken to investigate immune tolerance mechanisms in minor antigen-mismatched allogeneic BM chimeras when host-type BM was added to the BM inoculum.

METHODS

C3H (H2k, Thy 1.2, Mls 2a) recipients were conditioned with 9.5 gray (Gy) of total body irradiation. To exclude any interference with possible subclinical GVHD, 5x10(6) TCD AKR (H2k, Thy 1.1, Mls 1a) BM cells were injected with (syn + allo) or without (allo) 5x 10(6) TCD C3H BM cells. Chimerism, clonal deletion, and T lymphocyte subsets were scored using FACS and anti-mouse Thy, Vbeta6, Vbeta3, CD3, CD4, or CD8 monoclonal antibodies. The stability of tolerance was studied by investigating mixed lymphocyte reaction and cytotoxic T cell induction in chimeras after immunization with host, donor, or third-party (BALB/c) splenocytes. Breaking of chimerism was attempted by injecting nontolerant 40x10(6) host-type splenocytes 2 months after BM transplantation. Cytokines and Valpha14 mRNA were assayed using real time quantitative reverse transcriptase-polymerase chain reaction at 4 and 48 hr, respectively, after injection of nontolerant host-type splenocytes.

RESULTS

Both groups of mice became long-term stable mixed chimeras without any clinical sign of GVHD. Neither group was able to produce antihost nor antidonor cytotoxic T cells, even after immunization. The addition of syngeneic BM to the allogeneic inoculum reduced the overall level of allogeneic chimerism (from approximately 70% or approximately 85% in peripheral blood lymphocytes and spleen, respectively, in allo chimeras versus approximately 35% and approximately 60% in syn + allo chimeras). Moreover, it resulted in complete clonal deletion of both host-reactive (Vbeta3) and donor-reactive (Vbeta6) lymphocytes in syn + allo chimeras in contrast to in allo chimeras, in which only donor-reactive lymphocytes were completely deleted. After nontolerant C3H splenocyte injection, high levels of interleukin 2 mRNA were produced and chimerism decreased in syn + allo chimeras. In contrast, in allo chimeras, this maneuver was followed by the production of higher levels of interleukin 4 and interferon-gamma, and of Valpha14 mRNA, as well as by the proliferation of CD3+CD4-CD8- (double-negative) T cells and by an increase of donor chimerism.

CONCLUSION

The addition of host-type BM to the allogeneic inoculum has an influence on the level of chimerism, the extent of clonal deletion, and the reaction of chimeras after the injection of nontolerant host-type splenocytes. In the latter phenomenon, cytokine production and proliferation of Valpha14+ CD3+CD4-CD8- (double-negative, natural killer T) lymphocytes may be involved.

Discordant xenogeneic neonatal thymic transplantation can induce donor-specific tolerance

The limited supply of human organs for transplantation necessitates the development of methods leading to acceptance of xenografts. To avoid the hazards of the high-dose chronic immunosuppressive pharmacotherapy which would otherwise be required for successful xenografting, it would be desirable to induce permanent tolerance to xenogeneic donors. We have recently demonstrated that xenogeneic donor-specific tolerance can be induced by transplanting fetal pig thymic and hematopoietic tissue into thymectomized, T cell-depleted, and natural killer-cell-depleted mice, or into natural killer cell-depleted nude mice. We have now extended these studies by replacing fetal tissue with neonatal pig thymic and hematopoietic tissue, and by examining the in vivo responses of reconstituted mice to pig skin grafts. Neonatal tissue was studied because it might be more practicable than fetal tissue for the purpose of transplantation to primates. BALB/c nu/nu mice transplanted with neonatal (<24-hr-old) pig thymus and spleen fragments developed circulating mouse CD4+ cells. The pig thymus grafts were necessary for mouse T-cell development, as CD4 recovery did not occur in recipients of neonatal pig splenic tissue alone. The CD4+ cells that developed included Vbeta8.1/2+ T cells in similar proportions as in BALB/c mice, and Vbeta11+ and Vbeta5+ CD4 T cells were deleted almost as completely as in normal BALB/c mice. This deletion was detected among CD4 single-positive graft thymocytes. In 9 of 12 evaluable animals, mixed lymphocyte responses demonstrated tolerance to donor-type pig SLA antigens, with responsiveness to alloantigens and/or third-party pig xenoantigens. Furthermore, grafting of neonatal pig thymus conferred the ability to reject allogeneic mouse skin in 7 of 10 animals. In addition, 7 of 10 animals accepted paternal (donor SLA-matched) skin (median survival time [MST] > 100 days), whereas 4 of 4 animals rejected third-party SLA-mismatched pig skin (MST=40.5 days). We conclude that neonatal pig thymi transplanted to BALB/c nu/nu mice can support the development of mouse CD4+ cells that are functional and specifically tolerant to donor-type pig antigens.

Efficient immune responses in mice lacking N-region diversity

Mice with a null mutation in the terminal deoxynucleotidyl transferase (TdT) gene harbor immunoglobulin and T cell receptor repertoires essentially devoid of N-region diversity. Consequently, the CDR3 loops important for antigen recognition are shorter and considerably less diverse than those of wild-type controls. We find surprisingly normal immune responses in TdT0 mice, as regards both efficiency and specificity. This provokes a reconsideration of the assumption that N-region diversity is required for an effective T and B cell repertoire.

Inhibition of the development of immediate hypersensitivity by staphylococcal enterotoxin B

We investigated the ability of staphylococcal enterotoxin B (SEB) to modify the immediate hypersensitivity response induced in BALB/c mice following sensitization to ovalbumin (OVA), a response mediated by OVA-reactive V beta 8 T cells. Mice were sensitized by skin painting with OVA every second day over a period of 2 weeks. SEB, a potent activator of V beta 8+ T cells, was administered at the same site where OVA was applied (skin of the lower abdomen) following two different protocols. In protocol (A) SEB was injected intradermally 1 day before painting with OVA and on day 7; in protocol B, SEB was injected each time OVA was applied to the skin (eight times). SEB (but not SEA) altered the development of immediate hypersensitivity to OVA, as demonstrated by the reduction in allergen-specific IgE, decreased OVA-specific immediate skin test responsiveness, and prevented the development of increased airways responsiveness after bronchial challenge with OVA. Injections of SEB did not alter the proliferative responses of local draining lymph node cells or spleen mononuclear cells to OVA, indicating that administration of SEB did not inhibit the sensitization of OVA, but shifted the immune response away from an immediate type response (IgE/IgG1) to IgG2a, IgG2b and IgG3. Although both protocols of SEB treatment did not lead to a major deletion of the V beta 8 T cell population, they did reduce the proliferative response of V beta 8+ T cells to OVA. These data indicate that the bacterial toxin SEB is capable of modifying the immediate hypersensitivity response induced by OVA by altering the functional capacity of antigen-reactive V beta 8 T cells.

Differential patterns of T cell clonal deletion in neonatal H-2 tolerance and I-E/Mls induced self-tolerance

The pattern of clonal deletion of putative I-E-reactive (V beta 11) and Mls-reactive (V beta 3) T cells was evaluated and compared by cytofluorographic and immunohistochemical methods in a model of neonatal H-2 tolerance and in I-E- or Mls-bearing strains of mice which normally delete these cell populations (self-tolerance). The ontogeny of deletion of V beta 11+ cells was studied by evaluating thymic changes from birth until maturity in B10.S (H-2s/I-E-), B10.A (H-2k/d/I-E+) and B10.S mice intravenously infused at birth with (B10.SxB10.A)F1 lymphohaematopoietic cells. The reduction in V beta 11+ cells was most prevalent in the medullary region of the naive B10.A and neonatally injected B10.S animals and was corroborated by flow cytometry which demonstrated a marked reduction in single CD4 and CD8 positive B beta 11 T cells when compared to naive B10.S mice. However, immunohistochemistry illustrated that 'deletion' was never complete since V beta 11+ cells remained in the thymic cortex and splenic lymphoid follicles. By comparison, DBA/2 mice (Mlsc+ and previously documented to have decreased levels of V beta 3+ cells) showed a different pattern of deletion of V beta 3+ T cells than what was found for T cells bearing V beta 11 in animals deleting this population. DBA/2 thymi contained fewer thymic V beta 3- cells and there was more complete elimination of these cells, particularly in the periphery, by flow cytometry and immunohistology. The mice which do not delete V beta 3 cells (Mlsc-) showed that the majority of V beta 3- cells were located in the medulla with a few cells distributed in the cortical region. This pattern was notably different than the distribution of V beta 11 cells in thymi. Despite their location by histology, the majority of remaining V beta 3+ cells were dual CD4/CD8 positive (CD4+CD8+) by flow cytometric analysis. Our data illustrate that V beta 11 and V beta 3 T cells appear to be eliminated (i.e. 'deleted') at similar stages of maturation (single positive) during self-tolerance as well as in a neonatal H-2 tolerance model. However, the degree of elimination and the location of the cells remaining in these mice is dramatically different, depending on which T cell population is being evaluated and which deleting ligand is presented intrathymically. Thus, the accepted tenet of dual CD4+CD8+ cells localizing to the thymic cortex appears to have exceptions.(ABSTRACT TRUNCATED AT 400 WORDS)

Flexibility of the T cell receptor repertoire

Alternative T cell receptor (TcR) gene usage between mice of different Mls alleles has been demonstrated in a number of T cell responses. A clear illustration of a flexible TcR V beta usage in the same strain of mice remains to be established. Using a model system in which I-Ek-restricted T cells recognizing lambda repressor cI protein (cI) 12-26 and pigeon cytochrome c (pcc) 81-104 predominantly use V beta 3 in B10.A and B10.BR mice, and V beta 1 in Mls-2a-bearing A/J and C3H mice, we have first demonstrated that the hierarchy of TcR V beta usage can not be inferred from one strain of mice to the other. The presumed flexibility of V beta 3 to V beta 1 did not exist in B10.BR mice in the given responses. Instead, a switch of dominant TcR from V beta 1/V beta 3 to V beta 8 was identified in C3H and B10.BR mice. In contrast, there was an absolute rigidity in TcR repertoire usage in some mouse strains such as A/J. The lack of flexibility was not due to slow generating kinetics of replacing T cells; since A/J mice treated with staphylococcal enterotoxin A from birth on still responded poorly to cI 12-26 and pcc 81-104. Therefore, whether TcR V beta usage in a T cell response would be flexible or rigid is highly dependent on each strain of mice. However, even the plasticity seen in B10.BR mice is very limited and further tolerance of the V beta 8+ population results in non-responsiveness toward the given antigens.

Combined activation of murine lymphocytes with staphylococcal enterotoxin and interleukin-2 results in additive cytotoxic activity

This report demonstrates that in vitro activation of murine spleen cells with interleukin-2 (IL-2) or the bacterial superantigen staphylococcal enterotoxin A (SEA) results in different patterns of activation and function of cytotoxic cells. Lymphokine-activated killer activity and antibody-dependent cellular cytotoxicity (ADCC) are mainly mediated by IL-2 activated natural killer (NK) cells. SEA is the most powerful T cell mitogen known so far and retargets cytotoxic T lymphocytes (CTL) to tumors expressing major histocompatibility complex (MHC) class II in staphylococcal-enterotoxin-dependent cellular cytotoxicity (SDCC). Culture of mouse spleen cells with SEA led to expansion and activation of T cells, which demonstrated strong SDCC activity and some NK-like cytotoxicity after 5 days in culture. Cell sorting revealed that both CD8+ and CD4+ T cells mediated SDCC but the former were more effective. Phenotypic analysis showed that SEA preferentially stimulated and expanded T cells expressing T cell receptor V beta 11, in particular CD8+ T cells. Combined activation with SEA and IL-2 resulted in simultaneous induction of T and NK cell cytotoxicity. Moreover, IL-2 had additive effects on SEA-induced SDCC. Combined treatment with SEA and IL-2 might therefore be an approach to induce maximal cytotoxicity against tumors and to recruit both T and NK cells in tumor therapy.

Stimulation with specific antigen can block superantigen-mediated deletion of T cells in vivo

The T-cell response to pigeon cytochrome c peptide, residues 88-104 (pcytC), in B10.BR mice is mediated largely by cells bearing both V beta 3 and V alpha 11 variable regions of the T-cell antigen receptor. These cells are, therefore, reactive with the superantigen staphylococcal enterotoxin A (SEA). Recent reports have shown that in vivo exposure to superantigen can lead to deletion of superantigen-reactive T cells from the pool of mature T cells in the periphery. Here we show that upon cotreatment of animals with both SEA and pcytC, bulk deletion of the population of SEA-reactive cells is maintained, while the subpopulation of SEA-reactive T cells that also responds to pcytC is not deleted but instead proliferates in response to pcytC. These results are discussed with regard to mechanisms regulating the balance between T-cell tolerance and T-cell activation in vivo.

Development of T cells in SCID mice grafted with fetal thymus from AKR mice or F344 rats

To examine the development of T cells within an allogeneic or xenogeneic environment, we engrafted the fetal thymus from AKR mice or F344 rats under the kidney capsule of SCID mice (mTG and rTG mice). T lymphopoiesis developed in SCID mice 2 months after transplantation, although the ratio of CD4/CD8 in both experimental groups was different from that of normal control. T cells in mTG mice did not show in vitro proliferation or cytotoxicity against either host-type C.B-17 (H-2d) or donor-type AKR (H-2k) cells, while they exerted potent activities against third-party B10 (H-2b) cells. In contrast, T cells in rTG mice exhibited proliferation against both host-type C.B-17 and donor-type F344 rat cells. Consistently, graft-vs.-host disease symptoms developed in these mice and histological examination showed impressive infiltration of lymphocytes into the skin or into the mucosal layers of the stomach. Activated state of T cells in rTG mice was also evidence by the positive expression of interleukin-2 receptor. Taken together, fetal thymus appears to contain progenitor cells which are sufficient for in vivo reconstitution of T lymphopoiesis, but species-specific environment is important for the induction of tolerance. In mTG mice, V beta 6+ T cells reactive to donor Mlsa determinants and V beta 3+ T cells reactive to host Mlsc determinants were deleted, suggesting that tolerance was regulated mainly by clonal deletion. By contrast, V beta 11+ T cells reactive to Mlsf determinants were not deleted possibly due to the lack of their ligands.

Effects of intrathymic injection of organ-specific autoantigens, parietal cells, at the neonatal stage on autoreactive effector and suppressor T cell precursors

Thymectomy on day 3 after birth (3d-Tx) induces autoimmune gastritis (AIG) in 81%, and oophoritis (AIO) in 25% of BALB/c mice at the age of 2 to 3 months. Intrathymic, but not intraperitoneal injection of syngeneic parietal cells into sex-matched BALB/c mice within 24 h of birth resulted in almost complete prevention of the development of AIG in these mice in which 3d-Tx was performed. The prevention induced was parietal cell specific, since the development of AIO was not inhibited in female mice. Moreover, the injection of BALB/c liver cells, Mls-matched (BALB/c) and -disparate (DBA/2) B blasts which resulted in V beta 6 T cell deletion, as well as the injection of staphylococcal enterotoxin B failed to prevent the diseases. These findings suggested that recognition of an autoantigen in the thymus is necessary for the induction of tolerance, and that involvement of Mls-1 antigens in the pathogenesis of AIG, as has been suggested previously (Schwartz, R. H., Cell 1989. 57: 1073), was unlikely. T cells that suppress the development of organ-specific autoimmune diseases in 3d-Tx mice seem to maintain the unresponsiveness of autoreactive T cells at the periphery in normal mice. In agreement with our previous observations, we found that intraperitoneal (i.p.) injection of spleen cells from 3-month-old normal mice into 3d-Tx mice on day 10 after birth prevented the development of AIG, whereas spleen cells from age-matched AIG+ (mice with AIG) or AIG- (mice without AIG) 3d-Tx mice failed to do this. This implies that the suppressor cells probably affect the differentiation of effector-precursor to effector. In fact, these suppressor cells did not inhibit the adoptive transfer of AIG to nu/nu BALB/c mice by spleen cells from 3d-Tx mice manifesting AIG. By negative selection using monoclonal antibody and complement, it was confirmed that the phenotype of the suppressor cell was CD4. In contrast to 3d-Tx, 10d-Tx did not induce AIG, indicating the peripheralization of the suppressor cell by that time. On the other hand, intrathymic injection of parietal cells immediately after birth did not affect suppressor cell generation, implying that some T cells, including suppressor cells, escape thymus selection. We postulate that these cells correspond to the precursors of the autoreactive effector T cells and suppressor T cells that are present in normal mice.

Antigen recognition properties of mutant V beta 3+ T cell receptors are consistent with an immunoglobulin-like structure for the receptor

We examined the effect of mutations in the V beta portion of a pigeon cytochrome c (cyto c)-specific V beta 3+/V alpha 11+ T cell receptor on its ability to recognize cyto c/IEk and various superantigens. The results were consistent with an immunoglobulin-like structure for the receptor V beta domain and with separate interaction sites on V beta for conventional antigen and superantigens. An amino acid predicted to lie in CDR1 was critical for cyto c/IEk but not superantigen recognition, while several amino acids predicted to lie in the hypervariable region 4 loop were critical for superantigen but not cyto c/IEk recognition.

Dissociation of autoaggression and self-superantigen reactivity

Self-superantigens have been described as products of endogenous retroviruses of the mouse ('minor lymphocyte stimulating loci') that are capable of interacting without prior processing with conserved domains of TCR V beta chains, causing the activation and deletion of most T cells expressing products of determined V beta gene families [1-4]. The fact that superantigens activate a far higher percentage of T cells (1-20%) than conventional, peptidic antigens (< 0.1%) provides the methodological advantage that the degree of clonal deletion may be measured by the analysis of the TCR repertoire using appropriate anti-V beta antibodies. Although much information on the spatio-temporal organization of repertoire-purging has been gathered by virtue of self-superantigens, serious doubts exist as to the possibility that such structures serve as pathogenetically relevant autoantigens. Thus, certain inbred mice spontaneously develop autoimmune diseases, although they bear T-cell repertoires that appear to be purged from self-superantigen-reactive V beta products. In addition, therapeutic interventions targeted to V beta gene products that are not specific for self-superantigens are successful in preventing disease development. The lack of correlation between superantigen-related V beta deletions and autoimmune disease development is substantiated in further models of murine autoimmunity. Based on these observations, we formulate the hypothesis that self-superantigen-reactive T cells are not involved in the development of autoimmune diseases.

T cell receptor-mediated recognition of self-ligand induces signaling in immature thymocytes before negative selection

Shaping of the T cell repertoire by selection during intrathymic maturation involves T cell receptor (TCR) recognition of major histocompatibility complex/self-antigen complexes. In this communication, we studied the ability of minor lymphocyte stimulating (Mls) determinants to act as self-tolerogens in the selection of the T cell repertoire. We demonstrate that unprimed T cells from normal as well as TCR transgenic mice form Mls-specific conjugates with antigen-presenting cells, and that this TCR-ligand interaction leads to elevation of intercellular Ca2+ ([Ca2+]i). Peripheral T cells from TCR transgenic mice expressing receptors specific for self-Mls antigen show no reactivities to Mlsa. However, a proportion of immature thymocytes from these mice show specific binding and strong [Ca2+]i elevation in response to self-antigen-presenting cells, although these thymocytes do not proliferate. This self-reactivity of thymocytes is inhibited by antibodies specific for TCR, CD4, CD8, class II molecules, lymphocyte function-associated antigen 1, and intercellular adhesion molecule 1. These results demonstrate for the first time that before thymic negative selection, immature T cells can specifically interact with cells bearing self-antigen, and suggest that the resulting TCR-dependent signal transduction events provide a basis for negative selection of self-reactive T cells.

An exogenous mouse mammary tumor virus with properties of Mls-1a (Mtv-7)

The classical minor lymphocyte stimulating (Mls) antigens, which induce a strong primary T cell response in vitro, are closely linked to endogenous copies of mouse mammary tumor viruses (MMTV). Expression of Mls genes leads to clonal deletion of T cell subsets expressing specific T cell receptor (TCR) V beta chains. We describe the isolation and characterization of a new exogenous (infectious) MMTV with biological properties similar to the Mls antigen Mls-1a. In vivo administration of either Mls-1a-expressing B cells or the infectious MMTV (SW) led to an increase of T cells expressing V beta 6 followed by their deletion. Surprisingly, different kinetics of deletion were observed with the exogenous virus depending upon the route of infection. Infection through the mucosa led to a slow deletion of V beta 6+ T cells, whereas deletion was rapid after subcutaneous infection. Sequence analysis of the open reading frames in the 3' long terminal repeat of both this exogenous MMTV (SW) and of Mtv-7 (which is closely linked to Mls-1a) revealed striking similarities, particularly in the COOH terminus, which has been implicated in TCR V beta recognition. The identification of an infectious MMTV with the properties of a strong Mls antigen provides a new, powerful tool to study immunity and tolerance in vivo.

Molecular characterization of Mls-1

Recently a series of endogenous and exogenous superantigens have been described which have one common feature, namely, they lead to in vivo deletion and in vitro stimulation of T cells expressing particular T cell receptor V beta genes. The Mls antigens represent the prototypes of these molecules. We have mapped Mls-1 to the endogenous mammary tumor virus (MMTV) Mtv-7, while other SAG have also been associated with various MMTV. The open reading frame gene of the MMTV encodes the SAG. Thus, the new terminology MMTV sag has been proposed for this gene. Transfection experiments suggest that the expression of MMTV sag is tightly controlled, probably by a negative acting factor encoded within the open reading frame. Furthermore, a pronounced IL-4 effect is seen in the functional detection of the transfected Mtv-7 sag. Since this lymphokine does not influence the mRNA level of the endogenous or transfected MMTV genes, it is likely that it exerts its effect by increasing transcription of MHC class II genes, whose products are required for functional detection of Mls. We have identified one mouse strain, MA/MyJ, which has an Mls-1 phenotype but does not contain Mtv-7. The SAG activity of this strain was mapped to a new mammary tumor provirus, Mtv-43, not seen in other inbred strains. Sequence analyses revealed that the predicted amino acid sequences of the Mtv-7 and the Mtv-43 sag genes are very similar. This is particularly striking in the C-terminus, where all other MMTV sag sequences differ 100%. Thus, this region of the molecule seems to control the V beta specificity of SAG molecules. It is likely that the SAG expression provides an advantage for the infectious MMTV, probably by facilitating its transmission by T cells from the site of primary residence in the gut to its final destination, the mammary glands.

Reduction of lupus nephritis in MRL/lpr mice by a bacterial superantigen treatment

The effects of biweekly intravenous injections of Staphylococcus Enterotoxin B (SEB) into autoimmune MRL-lpr/lpr (MRL/lpr) mice were investigated. Rather than causing the expansion of V beta 8+ T cells, SEB administration resulted in the reduction V beta 8+, CD4-CD8- "double-negative" (DN) T cells. This was shown by FACS analysis as this putative pathogenic population was diminished in both spleen and lymph node. The symptoms of systemic lupus erythematosus (SLE) in MRL/lpr, which include high titers of anti-DNA antibodies and circulating immune complexes and proteinuria, were reduced in SEB-treated mice in a dose-dependent manner. The clinical parameters of SLE in MRL/lpr, which include lymph node hyperplasia and necrotic vasculitis, were suppressed in 50-micrograms SEB-treated mice. T cells bearing V beta 6 T cell receptor, which does not interact with SEB, were not reduced with SEB administration. Thus, disease suppression was associated with a specific reduction in the number of V beta 8+, DN T cells. These results implicate a possible therapeutic role of superantigen-based immunotherapy in V beta-restricted, T cell-dominated clinical syndromes.

Profound alteration in an alpha beta T-cell antigen receptor repertoire due to polymorphism in the first complementarity-determining region of the beta chain

Amino acid residues that are critical in maintaining the framework structure of immunoglobulin heavy- and light-chain variable (V) regions are strongly conserved in the V alpha and V beta proteins of the alpha beta T-cell antigen receptor (TCR alpha beta). Consequently, it has been proposed that TCR alpha beta has a conformation similar to that of an immunoglobulin Fab fragment and that the regions of the TCR homologous to the three immunoglobulin complementarity-determining regions (CDRs 1, 2, and 3) bind to the peptide antigen-major histocompatibility complex (MHC) molecule ligand. A single amino acid substitution in the predicted CDR1 of the V beta 3 protein of certain mouse strains dramatically altered TCR alpha beta usage in an antigen-specific MHC-restricted immune response but did not abrogate V beta 3 specificity for the superantigens minor lymphocyte stimulatory locus (Mls)c and staphylococcal enterotoxin A (SEA). The results confirm the importance of the V beta CDR1 in antigen-MHC molecule recognition, supporting the Fab-like structural model of TCR alpha beta, and provide further evidence that conventional antigen-MHC recognition and superantigen recognition are mediated by distinct regions of the TCR beta chain. They also suggest that allelic polymorphism may be a significant source of diversity in the TCR repertoire.

Identification of a limited T-cell receptor beta chain variable region repertoire associated with diabetes in the BB rat

Diabetes-prone BB rats spontaneously develop type 1 diabetes due to a T-cell-dependent destruction of insulin-producing beta-islet cells. A number of T-cell abnormalities including lymphopenia, poor cell-mediated responsiveness to alloantigen, and an absence of an RT6+ T-cell subset are associated with disease susceptibility. Our previous studies have implicated the thymic antigen-presenting cell in influencing disease potential and responsiveness to alloantigen. Since this cell type is also known to influence T-cell receptor expression in developing thymocytes, we examined the thymic and peripheral T-cell receptor beta chain variable region repertoire in diabetes-prone and diabetes-resistant rats. Our findings indicate that animals susceptible to diabetes induction have a characteristic and limited peripheral beta chain variable region repertoire that differs markedly from that expressed in the thymus.

Mechanisms of IgE tolerance: dual regulatory T cell lesions in perinatal IgE tolerance

The mechanisms of genetic control of IgE responses are exercised at different immuno-physiological levels. This study centered upon the development of IgE lineage-specific regulatory T cells. Herein, we demonstrate the following points: (a) perinatal administration of soluble self IgE molecule or self IgE complexed with foreign antigen induces IgE tolerance as manifested by antigen-specific IgE unresponsiveness and a generalized IgE immunodeficiency, and the induction of IgE tolerance does not affect antigen-specific IgG1, IgG, and IgA responses; (b) inducibility of perinatal IgE tolerance is correlated with complete absence of endogenously secreted IgE in the neonates; and the state of persistent IgE tolerance also does not correlate with the presence of high levels of circulating anti-IgE autoantibodies; (c) The lesions induced during the ontogeny of IgE antibody system do not appear to result from an imbalance of production of interleukin 4 and interferon-gamma by T helper Th2 and Th1 cells in antigen-stimulated cultures; the dual immunoregulatory lesions in T cell subsets are demonstrated: clonal anergy/deletion of CD4+ IgE Th cells and the presence of CD8+ IgE suppressor cells induced by perinatal IgE treatment. We propose that antigen/interleukin 4 activated B cells are controlled by IgE lineage-specific regulatory T cells which recognize self IgE determinant(s) on IgE committed B cells. Life-long IgE tolerance ensues as a result of a new steady state of IgE lineage-specific CD4+ and CD8+ T cell subsets.

Analysis of the immune system with transgenic mice: T cell development

Transgenic mice carrying functionally rearranged T cell receptor genes have contributed significantly to our knowledge of T cell development and thymic positive and negative selection processes. In addition, TCR-transgenic mice have been used to investigate mutations affecting thymocyte development, like scid and lpr. Gene targeting by homologous recombination will allow to analyze more specifically the molecular mechanisms underlying thymic selection and peripheral tolerance.

Genetic dissection of T cell receptor V beta gene requirements for spontaneous murine diabetes

It has been demonstrated, in certain autoimmune disease models, that pathogenic T cells express antigen receptors of limited diversity. It has been suggested that the T cells responsible for the pathogenesis of type I diabetes mellitus might similarly demonstrate restricted T cell receptor (TCR) usage. Recently, attempts have been made to identify the V beta subset(s) that initiates and/or perpetuates the antiislet response in a mouse model of spontaneous autoimmune diabetes (non-obese diabetic [NOD] mice). In studies reported here, we have bred NOD mice to a mouse strain that congenitally lacks approximately one-half of the conventional TCR V beta alleles. Included in this deletion are TCR V beta gene products previously implicated as being involved in the pathogenesis of NOD disease. By studying second backcross-intercross animals, we were able to demonstrate that this deletion of TCR V beta gene segments did not prevent the development of insulitis or diabetes.

An additional hypervariable region encoded by V gene segments occurs in Tcr V beta at a location compatible with its involvement in Tcr active site--a general model for alloreactivity

The number of V alpha and V beta sequences of T cell receptors now available allows a meaningful analysis of their variability profiles. Variability plots were derived using a modified form of Wu and Kabat's algorithm: variability is not computed as a proportion of the number of different residues occurring at a position, but rather proportionally to the physicochemical differences between the different residues. Results show that the classical hypervariable regions occurring in immunoglobulins also occur in T cell receptors at equivalent positions. Contrary to immunoglobulins the framework of Tcr V regions displays many relatively variable regions and positions. This phenomenon can be connected with the genetic organization of V genes of T cell receptors which seem to avoid any framework homogenization and the resulting gene conversion. More importantly an additional hypervariable region was detected in V beta but not in V alpha. This fourth hypervariable region is located between the second and the D hypervariable CDR. The predicted three-dimensional location of this additional hypervariable region is compatible with a possible role in antigen recognition and therefore also in positive and/or negative selection. Furthermore our data suggest that this fourth hypervariable region is involved in the recognition of superantigens like bacterial enterotoxins. Indeed this additional hypervariable region is not detected when variability is derived using an alignment of the V beta subgroups stimulated by one toxin of S. aureus. Finally we propose a new and simple molecular model to explain alloreactivity as crossreactivity between the universe of shapes (isomers of conformation) of different MHC haplotypes.

The T cell receptor repertoire influences V beta element usage in response to myoglobin

T cell clones recognizing the sperm whale myoglobin (SpWMb) epitope 110-121 in association with H-2d major histocompatibility complex class II molecules display a very limited heterogeneity of T cell receptor (TCR) V beta usage in DBA/2 mice. All clones previously tested used the same V beta 8.2 gene segment and very restricted junctional regions. To investigate the significance of this observation in vivo, we immunized DBA/2 mice with the intact SpW Mb protein or peptide 110-121. Only the V beta 8+ T cells showed any significant response to the 110-121 epitope. The response to peptide 110-121 was then analyzed in mice which, either as a consequence of antibody depletion or through genetic deletion of TCR V beta genes, lacked V beta 8+ peripheral T cells. DBA/2 mice depleted of V beta 8+ T cells by antibody treatment responded poorly to the 110-121 peptide, and only at high antigen concentrations. In contrast, DBA/2V beta a mice (homozygous for a deletion of multiple V beta gene segments including the V beta 8 family) made a response at least as great as that made by DBA/2 mice, even though the DBA/2V beta a mice had a very restricted TCR V beta repertoire compared with DBA/2 mice. Mechanisms which might determine differences in the 110-121 specific response of DBA/2, DBA/2V beta a and F23.1-treated DBA/2 mice are discussed.

The T-cell repertoire is not dictated by self antigens alone

The influence of genetic and environmental factors on the functional cytotoxic T cell (CTL) allorepertoire was studied by comparing the CTL precursor frequencies against the same HLA alloantigens in 116 sibling pairs. A significantly different precursor frequency was found in 68%, 61% and 59% of siblings sharing 0, 1 and 2 HLA haplotypes, respectively. These data show that, although HLA is important in determining the T-cell repertoire, this is hardly reflected in the allorepertoire. Even 50% of the monozygotic twin pairs showed a significant disparity in their CTL allorepertoire, indicating that environmental factors play a role as well. The non-inherited maternal HLA antigens could be identified as one of the environmental factors shaping the CTL allorepertoire.

Thymic stromal cells in culture. I. Establishment and characterization of a line which is cytotoxic for normal thymocytes and produces hematopoietic growth factor(s)

Lines of thymic stromal cells have been established. One of these, designated TS-9, has been cloned and studied extensively. This line expresses both acid and alkaline phosphatases. Despite repeated cloning, TS-9 cells remain morphologically heterogeneous. The origin of these cells is not clear. They express low levels of immunologically identifiable cytokeratins, produce laminin, a basement membrane protein, but express antigens typically found on bone marrow stromal cells. The TS-9 cells are MHC Class I+ but Class II-. They express the Thy-1, Pgp-1, and Mac-2 antigens but not other lineage markers of T cells or macrophages. Coculturing TSC with normal thymocytes or with the CTLL-1 cell line leads to a profound inhibition of lectin-induced and/or IL-2 induced T cell proliferation. This requires direct cell-cell contact and ultimately results in the death of the bound lymphocytes. It cannot be reproduced by culturing the thymocytes with TSC culture supernatants. These supernatants do contain hematopoietic growth factor(s) which augment the growth of some T lineage cells and support the growth of monocytic colonies in semi-solid culture medium. Both normal thymocytes and a variety of T cell tumors bind to TSC but only the normal cells are killed as a consequence of this interaction. Neither the binding nor the killing appear to be MHC restricted. We suggest that this killing may provide a model for the effector mechanism of the negative selection imposed by the thymus on developing T cells.

Repertoire development and ligand specificity of murine TCR gamma delta cells

During the past several years, we have been studying the circulating TCR gamma delta cells expressed in peripheral lymphoid tissues. Biochemical and molecular characterization of the TCR gamma delta heterodimers present on these TCR gamma delta cells identified 3 TCR gamma proteins, V gamma 2-C gamma 1, V gamma 1.2-C gamma 2, and V gamma 1.1-C gamma 4. In addition, at least 6 different V delta gene products (V delta 2,4,5,6,V alpha 10, V alpha 11) are expressed in peripheral lymphoid tissue. Nucleotide sequence analysis has revealed a great deal of junctional diversity present among the different V gamma and V delta proteins. Thus, compared to other nonlymphoid tissues (e.g., skin), this population of TCR gamma delta cells appears quite extensive. The development and specificity of TCR gamma delta cells has been pursued by two approaches. First, different TCR gamma delta cells clones were generated which recognize MHC-encoded gene products. One clone recognizes an unconventional TL-encoded antigen, whereas others have been shown to recognize either classical MHC class I or class II antigens. The TCR gamma delta receptor genes have been cloned from the TL-specific TCR gamma delta cell and used to construct transgenic mice to examine the development of TCR gamma delta cells. Although the Tg+ TCR gamma delta cells are tolerized by thymic clonal tolerance similar to TCR alpha beta cells, the epithelial Tg+ TCR gamma delta cells are subjected to non-deletional tolerance (anergy). A second approach towards examining the development of TCR gamma delta cells has been to compare the repertoire of TCR gamma delta splenocytes in a variety of inbred and MHC-congenic strains of mice using subset-specific anti-murine TCR gamma delta mAb. The percentage of individual subsets of splenic TCR gamma delta cells differ widely between different inbred strains of mice due to both MHC- and TCR-encoded genetic differences. In summary, these studies provides a basis for understanding and determining the ligand(s) of the TCR gamma delta heterodimer and the factors which shape the peripheral TCR gamma delta repertoire.

A potential role for microbial superantigens in the pathogenesis of systemic autoimmune disease

We have attempted herein to demonstrate how microbial superantigens could promote an abnormal form of "cognate" T helper-B cell interaction, analogous to that which may occur during GVH disease, leading to B cell activation and systemic autoimmunity. In vitro studies performed at our laboratory and others have demonstrated that resting human B cells bind microbial superantigens and present them to superantigen-reactive autologous T helper cells, resulting in T cell activation and polyclonal IgM and IgG production by the superantigen-bearing B cells. In vitro studies of microbial superantigen-mediated murine T helper-B cell interactions demonstrate preferential help for B cells that have encountered specific antigen. Both in humans and in mice, the cellular interactions involved and the B cell responses induced are highly analogous to those mediated by allospecific T helper-B cell interaction. Finally, the results of studies carried out on T cell-deficient (nude) mice suggest that microbial superantigens may trigger similar T helper cell-dependent polyclonal IgM and IgG responses in vivo. These mice will be studied over time and tested for the development of autoantibodies characteristic of SLE and of autoimmune organ system damage, the occurrence of which are predicted by our model.

Self-reactive T cells are activated by the 65-kDa mycobacterial heat-shock protein in neonatally thymectomized mice

To elucidate the mechanism of autoimmune disease in neonatally thymectomized (NTX) mice, we have investigated the responsiveness of the self-reactive T cells which have not undergone clonal deletion in such animals. Consistent with a recent report (Yuuki et al., Eur. J. Immunol. 1990. 20: 1475), T cells bearing V beta 11-gene products capable of recognizing I-E-encoded molecules were readily detected in the mature T cell pool of NTX BALB/c (I-Ed, Mls-2a) mice. The V beta 11-bearing T cells in NTX mice expressed interleukin 2 receptors and responded normally to signals delivered through the T cell receptor. Notably, these T cells in NTX mice proliferated significantly after culture with the 65-kDa mycobacterial heat-shock protein, whose amino acid sequence is highly homologous to that in eukaryotes. These results suggest that self-reactive T cells in NTX mice may be activated by heat-shock proteins derived from various pathogens and/or stressed autologous cells, resulting in the development of autoimmune diseases in such animals.

Distinct mechanisms of neonatal tolerance induced by dendritic cells and thymic B cells

To assess the role of different types of antigen-presenting cells (APC) in the induction of tolerance, we isolated B cells, macrophages, and dendritic cells from thymus and spleen, and injected these into neonatal BALB/c mice across an Mls-1 antigenic barrier. One week after injection of APC from Mls-1-incompatible mice or from control syngeneic mice, we measured the number of thymic, Mls-1a-reactive, V beta 6+ T cells and the capacity of thymocytes to induce a graft-vs.-host (GVH) reaction in popliteal lymph nodes of Mls-1a mice. Injection of thymic but not spleen B cells deleted thymic, Mls-1a-reactive V beta 6+ T cells and induced tolerance in the GVH assay. The thymic B cells were primarily of the CD5+ type, and fluorescence-activated cell sorter-purified CD5+ thymic B cells were active. Injection of dendritic cells from spleen or thymus also induced tolerance, but the V beta 6 cells were anergized rather than deleted. Macrophages from thymus did not induce tolerance. Dendritic cells and thymic B cells were also effective in inducing tolerance even when injected into Mls-, major histocompatibility complex-incompatible, I-E- mice, but only thymic B cells depleted V beta 6-expressing T cells. Therefore, different types of bone marrow-derived APC have different capacities for inducing tolerance, and the active cell types (dendritic cells and CD5+ thymic B cells) can act by distinct mechanisms.

Role of MHC and antigens in T-cell development

The role of self-peptides in influencing the development of the T-cell repertoire has been the focus of recent studies. The findings suggest that the recognition of self-peptides bound to MHC proteins in the thymus is part of the thymic self-recognition process that results in selective maturation, or positive selection of T cells.

Direct binding of secreted T-cell receptor beta chain to superantigen associated with class II major histocompatibility complex protein

The interaction of the T-cell receptor (TCR) with peptide antigen plus major histocompatibility complex (MHC) protein requires both alpha and beta chains of the TCR. The "superantigens" are a group of molecules that are recognized in association with MHC class II but that do not appear to conform to this pattern. Superantigens are defined as such because they cause the activation or thymic deletion of many or all T cells bearing specific TCR beta-chain variable region (V beta) elements. The strong association of particular V beta S with T-cell responses to superantigens suggests that their interaction with the TCR is fundamentally different from that of most antigens. We have directly investigated the involvement of the beta chain in recognition of a superantigen by using a secreted, truncated TCR beta chain and the bacterial superantigen staphylococcal enterotoxin A complexed to cell-surface MHC class II. We demonstrate that this interaction is specific for the enterotoxin and is dependent on MHC class II expression by the cell. The reaction can be inhibited by antibodies against the three components of the reaction: V beta, enterotoxin, and class II. This shows that the TCR beta chain is sufficient to mediate the interaction with a superantigen-class II complex. The TCR alpha chain and co-receptors such as CD4 are not required.

Defect in negative selection in lpr donor-derived T cells differentiating in non-lpr host thymus

Transplantation of bone marrow cells of lpr/lpr mice into irradiated normal mice fails to develop massive lymphadenopathy or autoimmunity but causes severe graft-vs.-host-like syndrome. To elucidate an abnormality of lpr/lpr bone marrow-derived T cells, we transplanted bone marrow cells of Mlsb lpr/lpr mice into H-2-compatible Mlsa non-lpr mice. Although lpr/lpr T cell precursors repopulated the host thymus as well as +/+ cells, a proportion of CD4+CD8+ cells decreased, and that of both CD4- and CD8- single-positive cells increased compared with those of +/+ recipients. Notably, in MRL/lpr----AKR and C3H/lpr----AKR chimeras, CD4 single-positive thymocytes contained an increased number of V beta 6+ cells in spite of potentially deleting alleles of Mlsa, whereas V beta 6+ mature T cells were deleted in the MRL/+ ----AKR and C3H/+ ----AKR chimeras. There was no difference between MRL/+ ----AKR and MRL/lpr----AKR chimeras in their proportion of V beta 3+ cells because both host and donor strain lack the deleting alleles. Interleukin 2 receptor expression of mature T cells, in the thymus and lymph node, was obviously higher in the MRL/lpr----AKR chimeras, in particular in the "forbidden" V beta 6+ subset. Moreover, lpr donor-derived peripheral T cells showed vigorous anti-CD3 response. These results indicate that lpr-derived T cells escape not only tolerance-related clonal deletion but also some induction of unresponsiveness in the non-lpr thymus.

Extrathymic tolerance of mature T cells: clonal elimination as a consequence of immunity

The mechanism by which T lymphocytes are tolerized to self or foreign antigens is still controversial. Clonal deletion is the major mechanism of tolerance for immature thymocytes; for mature T cells, tolerance is considered to reflect anergy rather than deletion, and to be a consequence of defective presentation of antigen. This paper documents a novel form of tolerance resulting when mature T cells encounter antigen in immunogenic form. Evidence is presented that exposure of mature T cells to Mlsa antigens in vivo leads to specific tolerance and disappearance of Mlsa-reactive V beta 6+ T cells. Surprisingly, the clonal elimination of V beta 6+ cells is preceded by marked expansion of these cells. Thus, tolerance induction can be the end result of a powerful immune response. These data raise important questions concerning the relationship of tolerance and memory.

V beta 17 gene polymorphism in wild-derived mouse strains: two amino acid substitutions in the V beta 17 region greatly alter T cell receptor specificity

Of 41 wild-derived mouse strains analyzed, 14 contained T cells bearing V beta 17 receptors in spite of the concomitant expression of I-E antigens. Reciprocal F1 and F2 hybrids of one of these strains, PWK, with laboratory strains revealed different patterns of V beta 17 T cell deletions from those observed with V beta 17 T cells from SJL, implying that the two V beta 17 regions are associated with recognition of distinct superantigens. The structures of the V beta 17 alleles differ by two amino acid substitutions, which lie together in an area distant from the predicted site of T cell receptor interaction with peptide-MHC complexes but overlapping with that implicated in V beta 8.2 recognition of Mls-1 superantigen. This demonstrates that the self-superantigen leading to V beta 17 T cell deletion varies with the allele of the receptor gene and confirms that T cell deletions by such ligands involve interactions with a region of the V beta domain that is distinct from the conventional combining site.

Selective anergy of V beta 8+,CD4+ T cells in Staphylococcus enterotoxin B-primed mice

The cellular basis of the in vitro and in vivo T cell responses to Staphylococcus enterotoxin B (SEB) has been investigated. The proliferation and cytotoxicity of V beta 8.1,2+,CD4+ and CD8+ T cells were observed in in vitro response to SEB. In primary cytotoxicity assays, CD4+ T cells from control spleens were more active than their CD8+ counterparts, however, in cells derived from SEB-primed mice, CD8+ T cells were dominant in SEB-specific cytotoxicity. In vivo priming with SEB abrogated the response of V beta 8.1,2+,CD4+ T cells despite the fact that these cells exist in significant number. This SEB-specific anergy occurred only in V beta 8.1,2+,CD4+ T cells but not in CD8+ T cells. These findings indicate that the requirement for the induction of antigen-specific anergy is different between CD4+ and CD8+ T cells in post-thymic tolerance, and the existence of coanergic signals for the induction of T cell anergy is suggested.

The requirement of intrathymic mixed chimerism and clonal deletion for a long-lasting skin allograft tolerance in cyclophosphamide-induced tolerance

Mechanisms of cyclophosphamide (CY)-induced tolerance were studied. When C3H/He Slc (C3H; H-2k, Mls-1b) mice were primed i.v. with 1 x 10(8) viable spleen cells from H-2-identical AKR/J Sea (AKR; H-2k, Mls-1a) mice and treated with 200 mg/kg of CY 2 days later, a long-lasting skin allograft tolerance to AKR was established. When [C57BL/6 Sea (B6; H-2b, Mls-1b) x AKR]F1 (B6AKF1) cells were used as the tolerogen, however, only a moderate, but not long-lasting, skin tolerance to AKR was observed. In the C3H mice treated with AKR cells and CY, the intrathymic clonal deletion of V beta 6+ T cells, which are strongly correlated with reactivity to Mls-1a antigens, was observed in the chimeric thymus on day 35, although neither the clonal deletion of V beta 6-bearing T cells nor the mixed chimerism was observed in the thymus on day 14. In the C3H mice treated with B6AFKF1 cells followed by CY, however, neither the clonal deletion of V beta 6+ T cells nor the mixed chimerism was observed in the thymus throughout the test period. In the lymph nodes of the C3H mice treated with AKR cells and CY, only CD4+ V beta 6+ T cells, bur not CD8+V beta 6+ T cells, had selectively decreased by day 14, and they were hardly detectable on day 35. The selective decrease of CD4+V beta 6+ T cells in the lymph nodes was also observed by day 14 when B6AKF1 cells were used as the tolerogen, although CD4+V beta 6+ T cells gradually increased on day 35, at which time almost all skin grafts from AKR had already been rejected. These results strongly support the necessity of the intrathymic mixed chimerism and clonal deletion of donor-reactive T cells for a long-lasting skin allograft tolerance in CY-induced tolerance.

Molecular analysis of the influences of positive selection, tolerance induction, and antigen presentation on the T cell receptor repertoire

Immunization of both B10.A and B10.S(9R) mice with pigeon cytochrome c (pcc) elicits T cells capable of proliferating to pcc presented on I-E major histocompatibility complex (MHC) molecules. The T cell receptor (TCR) repertoire used by pcc-specific T cells from these two strains is markedly different, even for T cells recognizing very similar antigen/MHC complexes. Our current studies have been directed toward explaining this differential expression between MHC congenic strains of TCR gene elements capable of recognizing similar ligands. Analysis of the TCR repertoire of pcc-specific T cells from F1[B10.A x B10.S (9R)]----parent radiation chimeras has demonstrated that much of this difference is a result of the positive selection of T cells for MHC restriction specificity. Further analysis of T cell lines from F1 mice and from radiation chimeras stimulated in vitro with pcc on both B10.A and B10.S(9R) antigen-presenting cells has provided clear-cut examples of the influence of positive selection, tolerance induction and of both in vivo and in vitro antigen presentation on the shaping of the TCR repertoire for a protein antigen. This is the first molecular analysis of how positive selection, tolerance induction, and antigen presentation can combine to mold the TCR repertoire.

Clonal anergy in self-reactive alpha/beta T cells is abrogated by heat-shock protein-reactive gamma/delta T cells in aged athymic nude mice

Although T cells proliferate and differentiate primarily in the thymus, athymic nude mice contain an appreciable level of T cell receptor alpha/beta and gamma/delta T cells, suggesting the existence of the extrathymic pathway in the development of both T cells. Recent studies with nude mice indicate that clonal deletion of self-reactive T cells does not occur extrathymically. In the present study, we have investigated the responsiveness of self-reactive T cells differentiating along an extrathymic pathway in aged BALB/c (H-2d, Mls-1b2a, I-E+, 7-8 month old) nude mice. Consistent with recent reports, T cells bearing V beta 3 or V beta 11, which are important for recognizing proteins encoded by the Mls-2a or the I-E allele, respectively, are readily detected in age nude mice. The V beta 3- or V beta 11-bearing T cells, however, do not proliferate in response to staphylococcal enterotoxin A which specifically stimulates V beta 3- or V beta 11-bearing T cells. When exogenous recombinant interleukin 2 was added to the culture, the V beta 3-bearing T cells in aged nude mice significantly proliferated in response to staphylococcal enterotoxin A. Aged nude mice also contained a substantial level of gamma/delta T cells which account for 15.6% of all Thy-1.2+ cells. The gamma/delta T cells proliferated and produced a significant level of interleukin 2 in response to the 65-kDa mycobacterial heat-shock protein, which is highly homologous to its eukaryotic counterpart. These results suggest that unresponsiveness of self-reactive T cells may be reversed by T cells responding to stress proteins expressed by the invading microbes and/or the stressed autologous cells.

Induction of neonatal tolerance to Mlsa antigens by CD8+ T cells

Antigen-specific tolerance of T cells to minor lymphocyte stimulatory (Mls) antigens can be induced in mice by neonatal injection of foreign lymphohematopoietic cells. Although immune responses to Mlsa antigens are controlled by B cells, CD8+ T cells were the most effective cell type for induction of Mlsa tolerance. Tolerance was evident in both thymus and lymph nodes and could be induced by as few as 2 x 10(4) CD8+ T cells; these cells were 50 to 100 times as potent as CD4+ cells or B cells in causing functional tolerance and deletion of V beta 6+ T cells. Thus, intrathymic contact with antigens expressed on CD8+ T cells may play an important role in controlling the normal development of tolerance.