Vβ11+ T-lymphocyte expansion by toxic shock syndrome toxin-1 differs in mice bearing H-2q versus H-2b haplotypes

We have recently demonstrated that toxic shock syndrome toxin-1 (TSST-1) expanded Vβ11⁺ T lymphocytes contribute to Staphylococcus aureus arthritis and sepsis-induced mortality. Interestingly, Vβ11⁺ T-cell mediated joint pathology varies in different mouse strains. In this study, we characterized the in vitro pattern of Vβ11⁺ T-cell expansion by TSST-1 in mice with various genetic backgrounds. Mice expressing major histocompatibility complex (MHC) class II I-E molecules did not expand Vβ11⁺ T cells upon stimulation with TSST-1. Using B10 congeneic I-E negative mouse strains, we found that the TSST-1-expanded Vβ11⁺ T cells in B10Q (H-2^q) and B10M (H-2^f) mice but not in B10B (H-2^b) mice. Antigen-presenting cells (APC) from B10Q mice, L cells and lymphoma cell line transfected with a q gene did not restore the deficient Vβ11⁺ T-cell expansion by TSST-1 in purified T cells from B10B mice. In contrast, I-A^b APC were able to stimulate Vβ11⁺ T cells from H-2^q mice. Furthermore, Vβ11⁺ T cells in H-2^b mice did expand when exposed to staphylococcal enterotoxin A (SEA). These findings suggest that the T-cell repertoire, skewed by clonal deletion and inactivation of self-reactive T cells, accounts for the different magnitude of Vβ11⁺ T-cell expansion among the different mouse strains.     

Binding of toxic shock syndrome toxin-1 to murine major histocompatibility complex class II molecules

The staphylococcal exotoxin toxic shock syndrome toxin-1 (TSST-1) has potent stimulatory effects on murine and human lymphocytes. This is the consequence of TSST-1 binding to major histocompatibility complex (MHC) class II molecules and the engagement in a V beta-restricted fashion of the T cell receptor by the TSST-1-MHC class II complex. Using radioligand and functional assays we have recently shown that TSST-1 binds to all HLA-DR (n = 14), HLA-DQ (n = 2) and HLA-DP (n = 2) phenotypes tested. In this study, we have examined the ability of murine MHC class II molecules to bind TSST-1. Specific high-affinity binding of TSST-1 was detectable to unfractionated BALB-c (H-2d) and C57BL/6 (H-2b), but not to C3H (H-2k) spleen cells. The Kd of this binding estimated from Scatchard analysis was in the same nanomolar range as the Kd of binding of TSST-1 to HLA-DR. Binding of 125I-labeled TSST-1 to BALB/c-derived B cell lymphoma lines and to L cell transfectants correlated with the expression of I-A molecules, but not with the expression of I-E molecules. Furthermore, I-A+, I-E- cells but not I-A-, I-E+ cells were able to support TSST-1-induced T cell proliferation. The binding affinity of TSST-1 for I-Ak appears to be much lower than for I-Ad. L cell transfectants expressing hybrid DR alpha: I-E beta k molecules, but not those expressing I-E alpha k: DR1 beta molecules, could bind TSST-1 and efficiently support TSST-1-induced T cell proliferation. This suggests that minor differences in the highly homologous I-E alpha and DR alpha chains are critical in determining the affinity of the MHC class II molecule for TSST-1. These results demonstrate that the binding of TSST-1 to MHC class II molecules in the mouse, in contrast to humans, is strongly influenced by phenotype. Analysis of the molecular basis of these differences may help to localize staphylococcal exotoxin binding sites on MHC class II molecules.     

Mouse intestinal epithelial cells express the self superantigen Mis1

In previous studies, we demonstrated that intestinal epithelial cells of the mouse small intestine could present exogenous antigen to specific CD4⁺ T cell hybridomas. We now report on the abililty of normal enterocytes to present the self superantigen M1sl^a. Enterocytes from M1sl^a but not from M1sl^b strains stimulated interleukin-2 production through aVβ6⁺ T cell hybridoma specific for M1sl^a determinants. Antibody inhibition experiments showed that enterocytes presented M is determinants via a major histocompatibility complex class II-dependent mechanism. Furthermore, the ability of enterocytes to activate Vβ6⁺ M1sl^a-specific T cells was inhibited by monoclonal antibodies against the Orf protein encoded by an Mtv-7 provirus which is associated with M1sl^a expression. These findings provide evidence for the first time that M is determinants are expressed on normal enterocytes and support the theory of a possible role of these cells in extrathymic selection of T cell receptor Vβ repertoire of intraepithelial T lymphocytes.     

Mls allo-determinants are recognized in an MHC class II antigen-dependent but unrestricted fashion by a discrete set of T cells

Blocking studies carried out with anti-H-2 class II antigen antibodies show that H-2 class II molecules are intimately involved in the recognition of Mlsa determinants by unprimed, specifically responsive T cells. The blocking of the anti-Mlsa response by these antibodies were not due to inhibition of IL-1 production by H-2 class II antigen positive macrophages. A strain analysis indicates that the response to Mlsa is regulated by H-2-linked genes and that this effect is exerted at the level of the stimulator cells; however, the response to Mls epitopes does not appear to be H-2 restricted. Finally, the ability of spleen cells from Mls-incompatible mice to induce a state of Mls-specific, clonal deletion type tolerance by neonatal injection, shows that Mls determinants exist in qualitatively allelic forms and suggests that these determinants are recognized by specific clones of T cells.     

Gene complementation in the T lymphocyte proliferative response to poly(Glu56Lys35Phe9)nFunctional evidence for a restriction element coded for by both the I-A and I-E subregions

The T lymphocyte proliferative response to poly(Glu⁵⁶Lys³⁵Phe⁹)_n (GLΦ) is under the control of two immune response genes, Ir-GLΦ-β and Ir-GLΦ-α, mapping in the I-A and I-E/C subregions of the major histocompatibility complex, respectively. Previous studies have demonstrated that in order to generate a response to GLΦ, both gene products must be expressed in the antigen-presenting cell (APC) but that neither responder allele has to be present in the responding T lymphocyte, provided that the T cell has matured in a responder environment. These results suggested that both gene products function as restricting elements in GLΦ presentation by APC. In this report, we provide further evidence for this model from experiments designed to test histocompatibility restrictions in antigen presentation at the I-E/C subregion. Genetic identity at the I-A subregion between T cells and APC was required for GLΦ presentation. To assess the requirements at I-E/C, B10. A(5R) T cells (I-A^b, I-E^k) primed to GLΦ were stimulated in vitro with GLΦ-pulsed spleen cells from F₁ hybrids between C57BL/10 (B10: I-A^b, I-E^b) which made the cells compatible at I-A, and a variety of B10 congenics bearing other H-2 haplotypes. Although none of the parental spleen cells could present GLΦ to B10.A(5R) T cells, spleen cells from F₁ hybrids between B10 and strains possessing H-2I of k, d, p and r presented GLΦ, whereas hybrids with strains possessing H-2I of f, q and s failed to present. This pattern of complementation for GLΦ presentation could not be explained on the basis of the responder status of the I-E/C donating parental haplotypes nor by invoking inhibitory stimuli from mixed lymphocyte reactions induced by the F_l APC. Rather, the pattern correlated with the presence of the serologic marker Ia.7 coded for by the I-E subregion of the complementing parental haplotype and the possession of an I-E-encoded a chain which has been shown by peptide mapping to be very similar in strains bearing the k, d, p and r haplotypes. These results suggest that the restriction element involved in the presentation of GLΦ to B10.A(5R) T cells is composed of a β chain encoded in I-A^b and an a chain encoded in I-E for which the allelic products of the k, d, p and r haplotypes are functionally equivalent. This correlation between structure and function represents the strongest evidence so far that Ia antigen-bearing molecules are the Ir gene products.     

Endogenous retroviral superantigen presentation by B cells induces the development of type 1 CD4+ T helper lymphocytes

The endogenous retroviral superantigen, minor lymphocyte stimulating antigen (Mls 1^a, encoded by Mtv-7), when presented by highly purified B cells induced the development of a highly polarized population of T helper (Th)1 cells from naive peripheral CD4⁺ T cells in vitro. Immobilized anti-Vβb6⁺ antibodies similarly generated highly polarized, largely Vβ6⁺, Th 1 populations in vitro. In the presence of exogenous interleukin-4, both stimuli were capable of generating Th 2, rather than Th 1 populations. Mls 1^a presentation by B cells in vivo led to the development of an equally polarized Th 1 population. Using monoclonal antibodies against interferon-γ and transforming growth factor-β it was demonstrated that maximal Th 1 development with either stimulus in vitro was dependent on the endogenous production of these two cytokines. Thus, our results demonstrate that the retroviral encoded superantigen, Mls 1^a, drives the development of Th 1 cells both in vitro and in vivo, and they suggest that B cell presentation does not, in itself, lead to the generation of Th 2 cells.     

Delineation of the minimal encephalitogenic epitope within the immunodominant region of myelin oligodendrocyte glycoprotein: diverse Vβ gene usage by T cells recognizing the core epitope encephalitogenic for T cell receptor Vβb and T cell receptor Vβa H-2b mice

The nature of the autoimmune T cell response to myelin oligodendrocyte glycoprotein (MOG), recently recognized as a potential target antigen in multiple sclerosis (MS), has not yet been characterized, in contrast to the T cell reactivity to other potential target antigens in MS such as myelin basic protein and proteolipid protein. Here, we show that the encephalitogenicity of the recombinant Ig-like domain of human MOG is associated, in H-2^b mice, with an immunodominant T cell reactivity against a single region of MOG spanning amino acids 35–55, accounting for the previously reported strong encephalitogenic activity of pMOG 35–55. A single injection of pMOG 35–55 with or without administration of pertussis toxin was sufficient to induce severe clinical experimental autoimmune encephalomyelitis (EAE) in H-2^b mice. Encephalitogenic pMOG 35–55-specific T cell lines derived from C3H.SW (Vβ^b) mice were diverse in their TCR Vβ gene usage (Vβ1, Vβ6, Vβ8 and Vβ15), although Vβ8.2 was most predominantly expressed (48%). However, Vβ8⁺ T cells may only be part of the encephalitogenic MOG-specific T cell repertoire in H-2^b mice, as demonstrated by the susceptibility of C57L (Vβ^a) mice to disease induced by pMOG 35–55. Encephalitogenic T cell lines from Vβ^a mice were also diverse in their TCR Vβ gene usage (Vβ1, Vβ2, Vβ6, Vβ14 and Vβ16). Such a heterogeneous TCR Vβ gene expression by pMOG 35–55/I-A^b-reactive T cells from both Vβ^a and Vβ^b H-2^b mice suggested multiple epitopes within pMOG 35–55. Analysis of the pattern of reactivity by pMOG 35–55-reactive T cells to a set of truncated peptides was not commensurate with independent nested epitopes, but revealed a requirement for recognition of a core sequence, YRSPFSRVV (pMOG 40–48). However, optimal stimulation was obtained with longer peptides, with each additional amino acid flanking either the N or the C terminus differentially increasing the stimulatory capacity of pMOG 40–48. Nonetheless, pMOG 40–48 was the minimal encephalitogenic epitope for both Vβ^a and Vβ^b mice. Thus, the T cell reactivity against the immunodominant encephalitogenic region of MOG is characterized by a diverse Vβ gene usage and a requirement for the same core epitope. This pattern of reactivity may favor epitope-directed, rather than TCR-targeted, approaches to immunospecific therapy for MOG-related autoimmune disease.     

Human HLA-DQ beta chain presents minor lymphocyte stimulating locus gene products and clonally deletes TCR V beta 6+, V beta 8.1+ T cells in single transgenic mice

Minor lymphocyte stimulating locus (Mls) gene products in association with mouse major histocompatibility complex (MHC) class II molecules are known to determine the repertoire of T-cell receptor (TCR) in mature T cells. In order to test whether human class II molecules can present mouse Mls, HLA-DQ beta transgenic mice were generated. The expression and function of the DQ beta transgene were studied in the progeny of one selected founder which was H-2f and H-2E negative. In these mice, DQ beta molecules pairing with mouse A alpha chain and invariant chain are expressed on the cell surface in a tissue-specific manner. When the DQ beta gene was bred into the Mls-1a strain DBA/1 (H-2q), T cells bearing V beta 6 and V beta 8.1 TCR were clonally deleted in the thymus of DQ beta+ transgenics but not in DQ beta-negative full sibs. Thus, the data presented here clearly demonstrate that the human MHC DQ beta chain can present Mls in the clonal deletion of T cells. Our results also suggest the requirement for an interaction between CD4 and class II molecules (alpha chain) for clonal deletion of T cells to occur.     

Influence of major histocompatibility complex haplotype on the mitogenic response of T cells to staphylococcal enterotoxin B.

The abilities of antigen-presenting cells (APC) from nine independent major histocompatibility complex haplotypes and a number of intra-H-2 recombinant congenic strains of mice to present staphylococcal enterotoxin B (SEB) and induce proliferation in murine T-cell receptor V beta 8+ T-cell clones were compared. SEB presented by APC of all haplotypes tested induced significant responses in each of the T-cell clones. The magnitude of response was similar for most haplotypes, but there were limited quantitative differences between certain haplotypes. SEB presented by APC from H-2b mice as well as the intra-H-2 recombinant strains B10.GD and B10.A(4R), which do not express cell surface I-E (designated I-E-), induced the poorest T-cell responses. However, APC from AfE-, AsE-, and AqE- mice were as potent in SEB presentation as APC expressing both I-A and I-E. Antibodies against I-E were more effective than anti-I-A antibodies at inhibiting responses to SEB presented by APC expressing both I-A and I-E, whereas responses induced by APC expressing I-A but not I-E were blocked by antibodies against I-A. Thus, our results show that I-A can present SEB efficiently but that expression of both I-A and I-E on the same APC results in presentation of SEB predominantly by I-E. In addition, experiments using four distinct I-E- strains of mice indicate that I-A alleles differ in their ability to present SEB.     

B-B cell interaction involved in polyclonal B cell activation is restricted by I-A but not by I-E molecules

We have previously demonstrated that the class II MHC restricted B-B cell interaction is involved in the polyclonal differentiation of unprimed murine B cells into IgM-producing cells induced by a T cell-derived lymphokine B151-TRF2 or bacterial LPS. The present study has addressed the question of whether I-A and/or I-E molecules function as restriction elements for the B-B cell interaction. The results revealed that (B10 x B10.BR)F1(H-2b/k) B cells could be separated into I-Ab- and 1-Ak-restricted subpopulations by their ability to bind to B10(H-2b) or B10.BR(H-2k) B cell monolayers, whereas an I-E-restricted F1 B cell population was not obtained. Moreover, B10-derived B cells isolated from (B10 + B10.BR) - (B10 x B10.BR)F1 but not from B10 - (B10 x B10.BR)F1 radiation-induced bone marrow chimeras acquired newly the ability to co-operate with mitomycin C-treated auxilary B cells expressing I-Ak but not I-Ek molecules. Thus, these results indicate that I-E molecules, unlike I-A molecules, do not serve as restriction elements for the B-B cell interaction, and that I-A and I-E molecules on B cells play functionally disparate roles in the activation of polyclonal B cells.     

The T/B cell interaction involved in induction of the mouse IgG2ah suppression is restricted by major histocompatibility complex class I,but not class II molecules

To determine the major histocompatibility complex (MHC) restriction of the T/B cell interaction involved in a negative regulation of Ig production, we used mouse model of T cell-induced IgG2a^b suppression in vivo. Normal or specifically triggered T splenocytes from mice of the Igh^a haplotype, when neonatally transferred into histocompatible Igh^a/b heterozygotes, are able to induce a specific and total suppression of the IgG2a^b allotype. Nevertheless, only transfer of IgG2a^b-primed Igh^a T splenocytes induces this suppression in Igh^b/b homozygous congenic mice in which the whole IgG2a isotype production is inhibited. This suppression is chronically maintained by CD8⁺ T cells, but can be experimentally reversed. We have established that the suppression induction required a CD4⁺CD8⁺ T cell cooperation and operated via the recognition by the involved TCR of Cγ2a^b-derived peptides presented by the target B cells in an MHC haplotype-restricted manner. Here, by using Igh^b mice genetically deficient for MHC class I (β2-microglobulin^%, or β2m^%) or class II (I-Aβ^%) molecules, we demonstrate functionally that the suppression induction implicates an MHC class I-, but not class II-restricted interaction. Indeed, the anti-IgG2a^b T cells transferred into Igh^b H-2^b I-Aβ^% mice carry out the suppression process normally, while in Igh^b H-2^b β2m^% recipients, their suppression induction capacity is significantly inhibited. Moreover, the Cγ2a^b 103–118 peptide, identified as the sole Cγ2a^b-derived peptide able to amplify the anti-IgG2a^b T cell reactivity in Igh^a H-2^b mice, is also able to stabilize the H-2D^b, but not the H-2K^b class I molecules at the surface of RMA-S (TAP2^?, H-2^b) cells. These results indicate that, despite the CD4⁺/CD8⁺ T cell cooperation during the induction phase of suppression only MHC class I molecule expression is required at the surface of IgG2a^b+ B cells for suppression establishment.     

Major histocompatibility complex control of the idiotypic network in the MOPC 173 system

Regulation of the anti-idiotypic response against MOPC 173 (M-173, γ_2a, ? myeloma of the BALB/c strain) was studied after syngeneic and allogeneic immunizations. The immunogen was M-173 polymerized with glutaraldehyde, and hemagglutinating titers (HT) were determined with sheep red blood cell-M-173. H-2 regulation of the response was clearly shown in mice having the same Igh-C^a genes as the immunogen protein. H-2^d mice (BALB/c) are dispersed responders (HT: 80-81 920) and 30% did not respond. H-2^k mice (BALB.K) are high responders (HT: 10240-81920), and H-2^b mice (BALB.B) are nonresponders (HT < 40). In animals of a non-BALB background, similar observations were made: Igh-C^a, H-2^k mice (C58) were responders, whereas Igh-C^a, H-2^b mice (C57L) did not respond. However, more dispersed HT values for the C58 animals as compared with those of the BALB.K suggest that a second level of regulation by background genes might be superimposed. When alloimmunization was used in strains not expressing the Igh-C^a allotype (b, e, j), animals responded whatever the H-2 haplotype (b, k, d). In this case, allotypic determinants might play a carrier role. All responder mice consistently made antiidiotypic antibodies as determined by hemagglutination and/or radioimmunoassay. Antibodies against new glutaraldehyde-induced determinants were also produced but appeared in low amounts in syngeneic immunizations. In allogenic immunizations, various levels of anti-allotype antibodies were detected. BALB.B (and BALB/c) mice are responders to U-10 (γ_2a,?, BALB/c myeloma), polymerized with glutaraldehyde and can respond to the M-173 idiotype when they are immunized with M-173 coupled to a heterologous carrier (a human γ₁, ? myeloma protein, Kle). The unresponsiveness of BALB.B mice to M-173 is thus idiotype-specific and is not due to a defect in the anti-idiotypic antibody repertoire. Injection of M-173 before M-173-Kle prevents the response to M-173 but not to Kle, which favors the occurrence of suppressive T cells. Responsiveness is dominantly transmitted in (BALB.B × BALB.K)F₁ mice which are Igh-C^a/a, H-2^b/k heterozygotes. Unresponsiveness found with the Igh-C^a, H-2^b combination is also observed in (BALB.B × B10)F¹ which are Igh-C^a/b, H-2^b/b. Since F₁ animals between BALB.B and B10.A (3R), (4R) or (5R) are all nonresponders, genes involved in the response to M-173 are not in the K, I-A, I-J, or I-E subregions. A participation of the I-B subregion or an I-A + I-E/C complementation cannot be excluded.     

Cross-reactive trinitrophenylated peptides as antigens for class II major histocompatibility complex-restricted T cells and inducers of contact sensitivity in mice. Limited T cell receptor repertoire

The induction of contact sensitivity in mice by hapten reagents such as trinitrochlorobenzene (TNCB) involves the activation of class II major histocompatibility complex (MHC)-restricted, hapten-specific, CD4⁺ T cells. Reports from different laboratories have indicated that the relevant antigenic epitopes in such reactions might include hapten-conjugated, MHC class II-associated peptides. This study for the first time directly demonstrates that hapten-peptides account for the majority of determinants recognized by trinitrophenyl (TNP)-specific CD4⁺ T lymphocytes. The sequences of those TNP carrier peptides do not have to be related to mouse proteins. Thus, we show that TNP-modified peptides derived from mouse IgG, pigeon cytochrome c or staphylococcal nuclease known to bind to I-A^b or from λ represser with specificity to I-A^d as well as TNP-proteins such as bovine serum albumin, ovalbumin or keyhole limpet hemocyanin all create class II-restricted hapten determinants for a number of TNP-specific T cell clones and hybridomas. All of these cells were induced with cells modified by trinitrobenzene sulfonic acid (TNBS). In addition, we present arguments indicating that individual TNP-specific helper T cells may cross-react with different TNP-peptides bound to identical class II molecules. Chemical treatment of antigen-presenting cells with TNCB or TNBS may thus result in a limited number of particularly repetitive immunodominant hapten epitopes. Immunodominant epitopes were also indicated by an overrepresentation of the TCR elements Vβ2 and Vα10 in I-A^b/TNP-specific T cells. Most importantly, however, we demonstrate that TNP attached to lysine 97 in the staphylococcal nuclease peptide 93–105 (i.e. a clearly “non-self” sequence) is able to prime mice for subsequent elicitation of contact sensitivity by TNCB in the absence of foreign protein. We take this to indicate that those TNP-peptide determinants defined by us as immuno-dominant are responsible for the induction of contact sensitivity to haptens.     

Evidence for quantitative and qualitative differences in functional activation of MIs-reactive T cell clones and hybridomas by antigen or TcR/CD3 antibodies

In this study, we demonstrated that some Vp6⁺, CD4⁺, Mls-l^a-specific T cell clones had cytolytic activity when stimulated with anti-T cell receptor(TcR)/CD3 monoclonal antibodies (mAb), but not with targets expressing Mls-1^a, although they produced lymphokines (interleukin 2 and interferon-y) in response to both types of stimuli. To examine the possibility that lack of cytolysis resulted from expression of the Mls-l^a antigen on merely a fraction of splenic B blasts, we (a) used the B cell lymphoma LBB.3.4.16 and (b) measured esterase secretion which is generally concurrent with cytotoxic T lymphocyte (CTL) activity. The B cell lymphoma maximally stimulated the T cell clone for interferon-y production when responding and stimulating cells were incubated at a 1:1 ratio, but it was never killed by the Mls-1^a-specific T cell clone unless TcR/CD3-specific mAb were added. Furthermore, a fivefold excess of the Mls-1^a B cell lymphoma did not induce any secretion of esterase, which was observed only in the presence of the TcR/CD3-specific mAb. Comparison of the reactivity of two Mls-1^a-specific T cell hybridomas expressing the same TcR at similar surface density, revealed both quantitative and qualitative differences between CD3-specific mAb and Mls stimulation of the hybridomas. A small quantitative difference in the sensitivity of hybridoma FJ22.5 to stimulation with V_β6 or CD3-specific mAb resulted in a marked decrease in efficiency of stimulation by Mls-1^a for interleukin 2 production and to inability to detect growth inhibition by Mls-expressing cells. A qualitative difference was observed when analyses of inositol phosphate production were performed under optimal conditions of stimulation of the highly responsive T cell hybridoma (FJ8.1): only stimulation with CD3-specific mAb, but not Mls-expressing cells, could induce detectable inositol phosphate production. Lack of cytolysis of Mls-1^a class II-expressing B cells may have evolutionary significance in view of the recent mapping of Mls to mouse mammary tumor virus genes.     

Clonal elimination of self reactive V beta 6+ T cells induced by H-2 products expressed on thymic radio-resistant components.

The role of thymic radio-resistant cells on clonal elimination of V beta 6+ T cells that are reactive to minor lymphocyte stimulatory (Mls)-1a plus I-E antigens has been investigated. Previous studies with allogeneic bone marrow chimeras revealed that radio-sensitive I-E+ cells derived from donor bone marrow in the thymus play a major role in the clonal elimination of V beta 6+ T cells. However, we could show that not only the thymic bone marrow derived components but also the radio-resistant ones (presumably thymic epithelial cells) might be involved in induction of clonal elimination of the self-reactive T cells. The proportion of V beta 6+ T cells present varied with the H-2 haplotype of the thymus and the cell types presenting Mls-1a products, which might be attributable to differences in the affinity of the H-2 products to T cell antigen receptors and differences in the amount of tolerogens expressed on the stromal cells.     

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-2^d) or donor-type AKR (H-2^k) cells, while they exerted potent activities against third-party BIO (H-2^b) 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 evidenced 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, Vβ6⁺ T cells reactive to donor Mls^a determinants and Vβ3⁺ T cells reactive to host Mls^c determinants were deleted, suggesting that tolerance was regulated mainly by clonal deletion. By contrast, Vβ11⁺ T cells reactive to Mls^f determinants were not deleted possibly due to the lack of their ligands.     

B lymphocyte activation upon exclusive recognition of major histocompatibility antigens by T helper cells

This study has investigated whether exclusive recognition of I-A or I-E molecules on the B cell surface by T helper cells is sufficient to activate resting B cells. Lines and clones of long-term-cultured T helper cells with specificity for I-A or I-E antigens have been derived from mixed lymphocyte cultures between spleen cells from major histocompatibility complex (MHC)-congenic mouse strains. These cells were tested for helper activity and proved competent to induce resting B lymphocytes expressing the specific MHC antigens to polyclonal expansion and maturation to Ig secretion. B cell activation was shown to require direct recognition of I-A/E antigens by the helper cells on the responding B lymphocyte surface and it could not be achieved by soluble factors released by "third-party" helper cell activity ongoing in the same cultures. Since B lymphocyte activation occurs in the absence of antigen recognition by the responding B cells, these observations suggest that I-A and I-E molecules expressed on the B cell surface participate in the functional reception of T helper cell-derived induction signals.     

A Vβ4-specific superantigen encoded by a new exogenous mouse mammary tumor virus

The superantigen (SAg) expressed by mouse mammary tumor virus (MMTV) has been shown to play an essential role in the course of the viral life cycle. In the present study, we describe a Vβ4-specific SAg encoded by a new exogenous MMTV carried by the SIM mouse strain. This is the first report of a viral or bacterial SAg reacting with mouse Vβ4⁺ T cells. Injection of MMTV(SIM) into adult BALB/c mice leads to a rapid and strong stimulation of Vβ4⁺ CD4⁺ T cells, followed by a slow deletion of these cells. Neonatal exposure to the virus also leads to a progressive deletion of Vβ4⁺ T cells. In contrast to other strong MMTV SAg, this new SAg requires the presence of major histocompatibility complex class II I-E molecules to be presented efficiently to T cells. Sequence analysis revealed a new predicted amino acid sequence in the C-terminal polymorphic region of this SAg. Furthermore, sequence comparisons to the most closely related SAg with different Vβ specificities hint at the specific residues involved in the interaction with the T cell receptor.     

Clonal expansion of T lymphocytes causes arthritis and mortality in mice infected with toxic shock syndrome toxin-1-producing staphylococci

Erosive arthritis is a common and feared complication of staphylococcal infection. The reason(s) for the progressive course of the arthritis is unknown. It has been recently established that enterotoxins produced by Staphylococcus aureus display superantigen properties leading to stimulation of T cells carrying distinct T cell receptor Vβ elements. This finding provides a potential connection between staphylococcal exoproteins and endogenous immune mechanisms participating in the infectious process. We have recently described successful induction of infectious arthritis in mice after intravenous inoculation of a toxic shock syndrome toxin-1 (TSST-1)-producing S. aureus LS-1 strain. Using this model we have now found a clonal expansion of T cells expressing Vβ11⁺ T cell receptor in the synovial tissue of arthritic mice. The role of TSST-1 as a superantigen inducing oligoclonal expansion was confirmed in an in vitro culture system. The expansion of Vβ11⁺ T cells proved to be of arthritogenic significance since mice genomically deleted of the Vβ11⁺ T cells did not develop arthritis and since pretreatment of healthy mice with anti-CD4 or anti-Vβ11 monoclonal antibodies inhibited arthritis. In addition, CD4⁺ and Vβ11⁺ T cells showed themselves to be of pathogenic significance in staphylococcal-induced mortality, since mice depleted of such populations showed increased survival. We propose that in hematogenously spread S. aureus-induced arthritis the TSST-1-dependent clonal expansion of CD4⁺ Vβ11⁺ T cells is a driving pathogenic force.