The T-cell repertoire is heavily influenced by tolerance to polymorphic self-antigens

Oligoclonal T cells in human cancer

Many solid tumors are characterised by the infiltration of lymphocytes and their presence has been correlated with a more favourable prognosis. These tumor-infiltrating lymphocytes (TIL), have been shown to possess specific cytolytic reactivity towards autologous tumours, thus suggesting that tumour cells may express antigens capable of eliciting an immune response. Expression of such tumour-associated antigens (TAA) in combination with appropriate accessory signals would lead to the in vivo accumulation of T cells with anti-tumour specificity. Analysis of the composition of the specific T-cell receptor (TCR) of TIL could thus provide information on the nature of the antigen(s) recognised by TIL. In this review, different aspects of the presence of clonal T cells in patients with cancer are discussed.

Idiosyncratic alterations of TCR size distributions affecting both CD4 and CD8 T cell subsets in aging mice

We have used a spectratyping method, which displays the size distribution for the complementarity-determining region 3 (CDR3) for T cells utilizing a specific TCR-Vbeta gene, to examine the effects of aging on the TCR repertoire of (BALB/c x C57BL/6)F1 hybrid mice. Although the size distributions from T cells of 8-month-old mice were typically symmetrically shaped around one or two bands of intermediate size, spectratypes from mice 16 or 24 months of age were frequently distorted, with specific size classes either over- or underrepresented compared to normal young controls. Each of 12 mice tested at 16 or 24 months of age had a skewed spectratype for at least one of the 24 Vbeta families examined, and some mice had more than 50% of their spectratypes skewed significantly, as judged by a chi2 test. Comparable age-associated skewing of the T cell repertoire occurred in the CD4 and CD8 subsets, and every mouse over 16 months of age exhibited at least one skewed Vbeta family in both the CD4 and CD8 populations. Although the mice were genetically identical and raised in common facilities, their spectratype patterns were nonetheless idiosyncratic: i.e., the specific set of abnormalities was distinct for each individual old mouse. Whether these distortions of the TCR repertoire in middle-aged and older mice lead to alterations in immune function remains to be determined.

Mtv-1 superantigen trafficks independently of major histocompatibility complex class II directly to the B-cell surface by the exocytic pathway

Presentation of the Mtv-1 superantigen (vSag1) to specific Vbeta-bearing T cells requires association with major histocompatibility complex class II molecules. The intracellular route by which vSag1 trafficks to the cell surface and the site of vSag1-class II complex assembly in antigen-presenting B lymphocytes have not been determined. Here, we show that vSag1 trafficks independently of class II to the plasma membrane by the exocytic secretory pathway. At the surface of B cells, vSag1 associates primarily with mature peptide-bound class II alphabeta dimers, which are stable in sodium dodecyl sulfate. vSag1 is unstable on the cell surface in the absence of class II, and reagents that alter the surface expression of vSag1 and the conformation of class II molecules affect vSag1 stimulation of superantigen reactive T cells.

A dominant V beta bias in the CTL response after HSV-1 infection is determined by peptide residues predicted to also interact with the TCR beta-chain CDR3

Many T cell responses are dominated by restricted TCR expression and can range from repeated usage of particular TCR Vbeta- and/or Valpha-elements, to the preferential usage of both V- and J-elements, often in conjunction with conserved V-D-J or V-J junctional sequences. Cytotoxic T lymphocytes specific for a Kb-restricted determinant from the herpes simplex virus glycoprotein B (gB) preferentially express a dominant TCRBV10 beta-chain with sequence conservation of a tryptophan-glycine located in the V-D junction. Here we have examined whether immunisation of C57BL/6 mice with the gB-peptide can mimic the CTL response seen after HSV-1 infection. Immunisation with the gB-peptide resulted in the generation of gB-specific CTL that showed a similar TCRBV10 bias to that observed after HSV-1 infection. When the gB-determinant was expressed as a part of a fusion protein, immunised mice again exhibited the TCRBV10 bias with the junctional sequence conservation in the responding CTL. C57BL/6 mice were then immunised with variants of the gB-peptide that contained amino acid substitutions at positions previously predicted to contact the TCR beta-chain CDR3. Analysis of the TCRBV usage of variant specific CTL lines showed that substitutions at the TCR-contact positions 4, 6 and 7 of the gB-peptide resulted in a loss of the TCRBV10 bias. These results suggest that the TCRBV10 bias seen in gB-specific CTL after HSV-1 infection is due to antigenic selection by the minimal peptide and is determined by residues proposed to contact the TCR beta-chain CDR3.

The role of the HLA-DQA1 gene in resistance to atrophic gastritis and gastric adenocarcinoma induced by Helicobacter pylori infection

BACKGROUND

It has been suggested that immunogenetic factors for susceptibility or resistance to disease caused by Helicobacter pylori exist in the host. To examine host genetic factors that increase the risk of gastric adenocarcinoma among H. pylori-infected persons, the HLA-DQA1 locus was examined in patients with gastric adenocarcinoma.

METHODS

Eighty-two gastric adenocarcinoma patients and 167 unrelated controls were examined for H. pylori infection and HLA-DQA1 genotyping. In addition, serum pepsinogen A (PGA) and pepsinogen C (PGC) values and the PGA/PGC ratio, which have been characterized as markers of gastric mucosal atrophy, also were analyzed.

RESULTS

Of the 167 controls, 121 were H. pylori positive (+) and 46 were H. pylori negative (-). All H. pylori (-) individuals had normal endoscopic and histologic findings. Among the 121 H. pylori (+) controls, 36 had superficial gastritis and 85 had atrophic gastritis. The allele frequency of DQA1*0102 was significantly lower in the H. pylori (+) atrophic gastritis group than in the H. pylori (+) superficial gastritis and H. pylori (-) normal control groups. In addition, the allele frequency of DQA1*0102 also was significantly lower in the H. pylori (+) intestinal type gastric adenocarcinoma group than in the H. pylori (-) normal control, H. pylori (+) superficial gastritis, and H. pylori (-) diffuse type gastric adenocarcinoma groups. Serum PGA and PGC values and the PGA/PGC ratio did not differ significantly among HLA-DQA1 genotypes; however, the PGA/PGC ratio was significantly lower in the H. pylori (+) atrophic gastritis and H. pylori (+) intestinal type gastric adenocarcinoma groups than in the H. pylori (-) normal control and H. pylori (+) superficial gastritis groups.

CONCLUSIONS

The DQA1*0102 allele may contribute to resistance against H. pylori-associated gastric atrophy and its association with intestinal type gastric adenocarcinoma, whereas the absence of DQA1*0102 may be a host genetic risk factor for H. pylori-associated atrophic gastritis and intestinal type gastric adenocarcinoma.

The role of the HLA-DQA1 gene in resistance to atrophic gastritis and gastric adenocarcinoma induced by Helicobacter pylori infection

BACKGROUND

It has been suggested that immunogenetic factors for susceptibility or resistance to disease caused by Helicobacter pylori exist in the host. To examine host genetic factors that increase the risk of gastric adenocarcinoma among H. pylori-infected persons, the HLA-DQA1 locus was examined in patients with gastric adenocarcinoma.

METHODS

Eighty-two gastric adenocarcinoma patients and 167 unrelated controls were examined for H. pylori infection and HLA-DQA1 genotyping. In addition, serum pepsinogen A (PGA) and pepsinogen C (PGC) values and the PGA/PGC ratio, which have been characterized as markers of gastric mucosal atrophy, also were analyzed.

RESULTS

Of the 167 controls, 121 were H. pylori positive (+) and 46 were H. pylori negative (-). All H. pylori (-) individuals had normal endoscopic and histologic findings. Among the 121 H. pylori (+) controls, 36 had superficial gastritis and 85 had atrophic gastritis. The allele frequency of DQA1*0102 was significantly lower in the H. pylori (+) atrophic gastritis group than in the H. pylori (+) superficial gastritis and H. pylori (-) normal control groups. In addition, the allele frequency of DQA1*0102 also was significantly lower in the H. pylori (+) intestinal type gastric adenocarcinoma group than in the H. pylori (-) normal control, H. pylori (+) superficial gastritis, and H. pylori (-) diffuse type gastric adenocarcinoma groups. Serum PGA and PGC values and the PGA/PGC ratio did not differ significantly among HLA-DQA1 genotypes; however, the PGA/PGC ratio was significantly lower in the H. pylori (+) atrophic gastritis and H. pylori (+) intestinal type gastric adenocarcinoma groups than in the H. pylori (-) normal control and H. pylori (+) superficial gastritis groups.

CONCLUSIONS

The DQA1*0102 allele may contribute to resistance against H. pylori-associated gastric atrophy and its association with intestinal type gastric adenocarcinoma, whereas the absence of DQA1*0102 may be a host genetic risk factor for H. pylori-associated atrophic gastritis and intestinal type gastric adenocarcinoma.

Efficient presentation of endogenous superantigen by H-2Aq

Endogenous superantigens encoded by mouse mammary tumor viruses associate with MHC class II and interact with T cells bearing particular V beta gene segments. H-2E is more efficient at presentation than H-2A, indeed Aq has not been shown to be capable of presenting endogenous superantigens. Atypically, the superantigen vSAG-3 encoded by Mtv-3 is presented efficiently in non-obese diabetic (H-2g7) mice by H-2A; we have examined the independent contributions of vSAG-3 and Ag7 to this process. Ag7 was not found to have a more general ability to efficiently present endogenous superantigens other than Mtv-3. Examination of Mtv-3-mediated thymic deletion of V beta 3+ thymocytes in the presence of H-2q additionally demonstrated the efficient presentation of vSAG-3 by Aq. Interaction of vSAG-3 with Aq and Ag7 is likely to reflect the unique sequence of Mtv-3 within the second polymorphic region previously implicated in MHC class II binding. The demonstration that mouse endogenous superantigens can be presented by a wider range of MHC haplotypes than previously thought is further evidence for their immunological impact on the mouse population.

A dominant interfering mutant of FADD/MORT1 enhances deletion of autoreactive thymocytes and inhibits proliferation of mature T lymphocytes

Members of the tumour necrosis factor receptor family that contain a death domain have pleiotropic activities. They induce apoptosis via interaction with intracellular FADD/MORT1 and trigger cell growth or differentiation via TRADD and TRAF molecules. The impact of FADD/MORT1-transduced signals on T lymphocyte development was investigated in transgenic mice expressing a dominant negative mutant protein, FADD-DN. Unexpectedly, FADD-DN enhanced negative selection of self-reactive thymic lymphocytes and inhibited T cell activation by increasing apoptosis. Thus signalling through FADD/MORT1 does not lead exclusively to cell death, but under certain circumstances can promote cell survival and proliferation.

TNF Receptor-Deficient Mice Reveal Striking Differences Between Several Models of Thymocyte Negative Selection

Central tolerance depends upon Ag-mediated cell death in developing thymocytes. However, the mechanism of induced death is poorly understood. Among the known death-inducing proteins, TNF was previously found to be constitutively expressed in the thymus. The role of TNF in thymocyte negative selection was therefore investigated using TNF receptor (TNFR)-deficient mice containing a TCR transgene. TNFR-deficient mice displayed aberrant negative selection in two models: an in vitro system in which APC are cultured with thymocytes, and a popular in vivo system in which mice are treated with anti-CD3 Abs. In contrast, TNFR-deficient mice displayed normal thymocyte deletion in two Ag-induced in vivo models of negative selection. Current models of negative selection and the role of TNFR family members in this process are discussed in light of these results.

Defect in Th1-like cells of nonresponders to hepatitis B vaccine

Peripheral blood lymphocytes from nonresponders to hepatitis B vaccine (HBsAg) failed to undergo a proliferative response to recombinant HBsAg in vitro, whereas cells from responders proliferated vigorously. The lack of proliferative response was not due to defective antigen presentation in that MHC-identical responder and nonresponder antigen presenting cells were equally effective in stimulating responder T cells. Nonresponder T cells did not proliferate in response to antigen-pulsed MHC identical responder antigen presenting cells. The present study demonstrated that: 1) there were no detectable (1 in < 20 x 10(4) HBsAg-precursor T cells in any of the nonresponders, while in responders the frequency of HBsAg-precursor T cells ranged from 1 in 3.2 x 10(3) to 1 in 40 x 10(3); 2) nonresponder cell cultures did not secrete IL-2 in response to HBsAg stimulation; 3) exogenous recombinant IL-2 did not restore the proliferative response of the T cells in HBsAg-pulsed cultures of nonresponders. These results suggest that the cellular basis for the lack of response to HBsAg is a defect in HBsAg-specific Th1-like cells; either there is an absence of the Th1 cells or cells with TCR specificity for HBsAg are present but are unresponsive to the HBsAg peptide-MHC complex (i.e., anergy or tolerance).

Oral administration of antigen does not influence the proliferation and IFN-γ production of responsive CD8+ T cells but enables to establish T cell clones with different lymphokine production profile

Feeding of a whole casein diet, which abolished the α(s1)-casein-specific proliferation and IFN-γ productivity of CD(4+) T cells, did not affect the proliferative response of CD8(+) T cells with regard to the antigen dose response, cell dose response, kinetics of the proliferation and epitope specificity, as well as IFN-γ production. To assess the characteristics of the CD8(+) T cells, we established α(s1)-casein-specific CD8(+) T cell clones from both casein-fed and control mice. The established clones produced different amount of IFN-γ and IL-10, and one clone derived from the casein-fed mice produced a remarkable amount of IL-10. The clones from casein-fed mice produced considerable amounts of TGF-β, while those from control mice produced only small amounts. The possible role of CD8(+) T cells in oral tolerance is discussed.

Interaction of pigeon cytochrome c-(43-58) peptide analogs with either T cell antigen receptor or I-Ab molecule

We determined that a pigeon cytochrome c-derived peptide, p43-58, possesses two anchor residues, 46 and 54, for binding with the I-Ab molecule that are compatible to the position 1 (P1) and position 9 (P9) of the core region in the major histocompatibility complex (MHC) class II binding peptides, respectively. In the present study to analyze each binding site between P1 and P9 of p43-58 to either I-Ab or T cell antigen receptor (TCR), we investigated T cell responses to a series of peptides (P2K, P3K, P4K, P5K, P6K, P7K, and P8E) that sequentially substituted charged amino acid residues for the residues at P2 to P8 of p43-58. T cells from C57BL/10 (I-Ab) mice immunized with P4K or P6K did not mount appreciable proliferative responses to the immunogens, but those primed with other peptides (P2K, P3K, P5K, P7K, and P8E) showed substantial responses in an immunogen-specific manner. It was demonstrated by binding studies that P1 and P9 functioned as main anchors and P4 and P6 functioned as secondary anchors to I-Ab. Analyses of Vbeta usage of T cell lines specific for these analogs suggested that P8 interacts with the complementarity-determining region 1 (CDR1)/CDR2 of the TCR beta chain. Furthermore, sequencing of the TCR on T cell hybridomas specific for these analogs indicated that P5 interacts with the CDR3 of the TCR beta chain. The present findings are consistent with the three-dimensional structure of the trimolecular complex that has been reported for TCR/peptide/MHC class I molecules.

Predominant T-cell receptor Vbeta usage of intraepithelial lymphocytes during the immune response to enteric reovirus infection

Previous studies have found that intraepithelial lymphocytes (IEL) contain virus-specific cytotoxic T lymphocytes (CTL) that increase dramatically during the course of virus infection. In the present study, the T-cell receptor (TCR) V beta pattern used by IEL against reovirus enteric infection was investigated both in conventional and in germfree mice. IEL were isolated by a modified rapid method, and their expression of 13 TCR V betas was examined by flow cytometric analysis. The virus-specific CTL activity of each TCR V beta subset was assessed by subtraction with coated Dyna beads by a nonradioactive assay. There was a preferential perturbation of TCR V betas following virus challenge, including increases in cells expressing V beta7, -12, -14, and -17 in conventional mice and V beta2, -12, and -17 in germfree mice. In conventionally reared mice, IEL maintained and restimulated in culture had a preferential use of TCR V beta9, -12, and -17. TCR V beta2 and -17 subfamilies were found amplified in all conditions. Furthermore, TCR V beta12 and -17 accounted for 37 and 77% of the virus-specific CTL activity, respectively, after in vitro restimulation. This study provides evidence that virus-specific CTL activity may be due to the oligoclonal expansion of TCR V beta subfamilies in IEL. Our findings suggest that in vivo infection selectively presents few T-cell epitopes and that the correct identification of these T-cell epitopes would increase the likelihood of success when designing subunit vaccines.

Mouse mammary tumor virus superantigens require N-linked glycosylation for effective presentation to T cells

Mouse mammary tumor viruses (MMTVs) encode superantigens that associate with major histocompatibility complex class II products on antigen-presenting cells and stimulate T cells in a V beta-specific manner. This T cell activation is critical for completion of the viral life cycle and vertical transmission to the next generation. To investigate the functional significance of extensive viral superantigen (Sag) glycosylation, we disrupted the six potential sites for N-linked carbohydrate addition in the Sag encoded by proviral integrant Mtv-1. Shifts in the apparent molecular mass of these mutant glycoproteins suggested that wild-type Mtv-1 Sag is glycosylated on four of its six sites. Intracellular and cell surface staining of the panel of mutants indicated that any decrease in glycosylation resulted in reduced levels of intracellular protein and undetectable surface expression, suggesting that decreased glycosylation leads to rapid Sag degradation and abates trafficking to the plasma membrane. Nevertheless, several mutants with intermediate levels of glycosylation expressed enough Sag on the B cell surface to potently stimulate reactive T cell hybrids. We show there is no specific site bearing N-linked glycosylation that is essential for activity, but at least one carbohydrate addition is necessary for effective B cell presentation of MMTV superantigens to T cells.

Viral superantigen drives extrafollicular and follicular B cell differentiation leading to virus-specific antibody production

Mouse mammary tumor virus (MMTV[SW]) encodes a superantigen expressed by infected B cells. It evokes an antibody response specific for viral envelope protein, indicating selective activation of antigen-specific B cells. The response to MMTV(SW) in draining lymph nodes was compared with the response to haptenated chicken gamma globulin (NP-CGG) using flow cytometry and immunohistology. T cell priming occurs in both responses, with T cells proliferating in association with interdigitating dendritic cells in the T zone. T cell proliferation continues in the presence of B cells in the outer T zone, and B blasts then undergo exponential growth and differentiation into plasma cells in the medullary cords. Germinal centers develop in both responses, but those induced by MMTV(SW) appear later and are smaller. Most T cells activated in the T zone and germinal centers in the MMTV(SW) response are superantigen specific and these persist for weeks in lymph nodes draining the site MMTV(SW) injection: this contrasts with the selective loss of superantigen-specific T cells from other secondary lymphoid tissues. The results indicate that this viral superantigen, when expressed by professional antigen-presenting cells, drives extrafollicular and follicular B cell differentiation leading to virus-specific antibody production.

CD8 T cells from major histocompatibility complex class II-deficient mice respond vigorously to class II molecules in a primary mixed lymphocyte reaction

Mature CD4+ and CD8+ T cells are restricted by major histocompatibility complex (MHC) class II and class I molecules, respectively. In a primary mixed lymphocyte reaction (MLR), CD8+ T cells from C57BL/6 (B6) mice can respond to allo-class I molecules, but not allo-class II molecules. However, a significant fraction of CD8+ T cells from C57BL/6 class II-deficient (B6Aalpha-) mice violate this rule by responding vigorously in a MLR to class II molecules. The frequency of responding cells is approximately 50% of that of B6 CD8+ T cells responding to B6bm1 allo-class I molecules. This response requires neither appropriate co-receptor, i.e. CD4, nor exogenous lymphokines, indicating that interactions between the T cell receptors (TCR) and class II molecules are remarkably efficient. Since these CD8+ T cells are positively selected by class I molecules in the thymus of class II-deficient mice, these CD8+ T cells should interact with both classes of MHC molecules. The absence of thymic negative selection by class II molecules may result in the production of these CD8+ T cells. The data imply that a substantial fraction of CD4+CD8+ double-positive thymocytes in wild-type mice interacts with both classes of MHC molecules prior to thymic selection.

Alternative pathways for the selection of antigen-specific peripheral T cells

In the thymus, maturing lymphocytes receive activation signals mediated by the T-cell antigen receptor (TCR) that either promote clonal survival (positive selection) or induce apoptosis (negative selection). This balance between life and death is mirrored by the sensitivity of cortical thymocytes to apoptotic death induced by antibodies against the CD3 component of the TCR signal-transduction complex, bacterial superantigens that bind to the TCR beta-chain, and corticosteroids. In contrast, mature peripheral T cells are positively activated by anti-CD3 antibody or superantigens and are resistant to steroid-induced death. Here we show that in splenic germinal centres, T cells regain thymocyte-like sensitivity to TCR- and steroid-induced apoptosis and undergo antigen-driven positive and negative selection. T-cell responses elsewhere in the spleen are unaccompanied by programmed cell death. Our observations define a new differentiation pathway for peripheral T cells and suggest that germinal centres induce a lymphocyte phenotype necessary for the maintenance of self-tolerance.

Inactivation of T cell receptor peptide-specific CD4 regulatory T cells induces chronic experimental autoimmune encephalomyelitis (EAE)

T cell receptor (TCR)-recognizing regulatory cells, induced after vaccination with self-reactive T cells or TCR peptides, have been shown to prevent autoimmunity. We have asked whether this regulation is involved in the maintenance of peripheral tolerance to myelin basic protein (MBP) in an autoimmune disease model, experimental autoimmune encephalomyelitis (EAE). Antigen-induced EAE in (SJL x B10.PL)F1 mice is transient in that most animals recover permanently from the disease. Most of the initial encephalitogenic T cells recognize MBP Ac1-9 and predominantly use the TCR V beta 8.2 gene segment. In mice recovering from MBP-induced EAE, regulatory CD4+ T cells (Treg) specific for a single immunodominant TCR peptide B5 (76-101) from framework region 3 of the V beta 8.2 chain, become primed. We have earlier shown that cloned B5-reactive Treg can specifically downregulate responses to Ac1-9 and also protect mice from EAE. These CD4 Treg clones predominantly use the TCR V beta 14 or V beta 3 gene segments. Here we have directly tested whether deletion/blocking of the Treg from the peripheral repertoire affects the spontaneous recovery from EAE. Treatment of F1 mice with appropriate V beta-specific monoclonal antibodies resulted in an increase in the severity and duration of the disease; even relapses were seen in one-third to one-half of the Treg-deleted mice. Interestingly, chronic disease in treated mice appears to be due to the presence of Ac1-9-specific T cells. Thus, once self-tolerance to MBP is broken by immunization with the antigen in strong adjuvant, TCR peptide-specific CD4 Treg cells participate in reestablishing peripheral tolerance. Thus, a failure to generate Treg may be implicated in chronic autoimmune conditions.

Mouse models of autoimmune disease suggest that self-tolerance is maintained by unresponsive autoreactive T cells

Multiple organ-localized autoimmune diseases, such as thyroiditis and gastritis, spontaneously develop in BALB/c nu/nu (nude) mice receiving embryonic rat thymus grafts (TG) under their renal capsules (TG nude mice). When thyroid was grafted into the rat thymus of TG nude mice, development of autoimmune thyroiditis, but not other diseases, was completely prevented. However, when such mice received thyroid antigen plus complete Freund's adjuvant (CFA), severe autoimmune thyroiditis developed, suggesting that some thyroid-specific autoreactive T cells migrate into the periphery, but remain unresponsive. Development of autoimmune diseases, including thyroiditis, in TG nude mice was prevented by a single intraperitoneal injection of splenic CD4+ cells from normal BALB/c mice and also from mice with intrathymic thyroid grafts, indicating that thyroid-specific suppressor T cells are present in normal mice and that such T cells are neither deleted nor inactivated by the intrathymic thyroid grafts, in contrast to autoreactive T cells. Thus clonal deletion in the thymus, and clonal anergy and/or ignorance in the periphery, of autoreactive cells is important to maintain immune tolerance to organ-specific antigen, but CD4 suppressor T cells may play a more important role in tolerance, and the failure of education of this population may cause autoimmune diseases in the TG nude mouse model.

Addition of corticosteroids to antibiotic treatment ameliorates the course of experimental Staphylococcus aureus arthritis

OBJECTIVE

To evaluate the combined effect of systemic corticosteroid and antibiotic therapy on the course of septic arthritis.

METHODS

The murine model of hematogenously acquired Staphylococcus aureus arthritis was used. Mice were treated with corticosteroids and antibiotics, and were followed up individually. Arthritis was evaluated clinically and histopathologically. Serum samples and bacterial isolates were also analyzed.

RESULTS

The prevalence of arthritis 14 days after the onset of the disease was 22% in the corticosteroid and antibiotic-treated group, as compared with 81% in the control (nontreated) group and 48% in the antibiotic-treated group. The severity of arthritis also decreased in the corticosteroid and antibiotic-treated group, as did the mortality rate. Immunohistochemical analysis revealed a dramatic decrease in T cells and macrophages in the synovium of mice that took the combined therapy. The mechanisms leading to this outcome include the inhibitory effect of corticosteroids on T cell and B cell proliferation and differentiation, such as suppression of interferon-gamma (IFN gamma) production. Serum levels of IFN gamma were decreased 4-fold in the antibiotic-treated group compared with the controls; a 15-fold decrease was observed in the corticosteroid and antibiotic-treated animals. In addition, serum NO3- was significantly decreased in mice treated with antibiotics (P < or = 0.05), as well as in mice treated with corticosteroids and antibiotics (P < or = 0.001).

CONCLUSION

Systemic corticosteroid administration along with antibiotic therapy had beneficial effects on the course and outcome of S aureus arthritis.

CD4 expression is important but not essential for infection with exogenous mouse mammary tumor virus

We studied local events in the popliteal lymph nodes of CD4-deficient mice following foot pad injection with an MMTV strain which carries the gene for a V beta 14-specific superantigen. Injection of the V beta 14-specific MMTV induced vigorous expansion of V beta 14+ CD4+ T cells and B cells in their lymph nodes of CD4+/- heterozygous control mice. On the other hand, CD4-/- mice injected with the MMTV showed a proliferation of V beta 14+ T cells among the population of TCR alpha beta + CD4-CD8- T cells, although to a lesser extent. This phenomenon was not accompanied by vigorous B cell expansion. A PCR assay revelated that the MMTV definitely infected the lymph nodes cells of the CD4-/- mouse. However, the infectivity of the MMTV in CD4-/- mice was approximately 20 times lower than that in CD4+/- mice. These findings indicate that, in MMTV infection of CD4-deficient mice, the superantigen-reactive T cells among the population of TCR alpha beta +CD4-CD8- T cells substitute for the superantigen-reactive CD4- T cells of normal mice, and that the absence of CD4 molecules decreased the infectivity of MMTV because of insufficient expansion of the superantigen-reactive T cells.

Immune response to mouse mammary tumour virus

Superantigens of mouse mammary tumor virus induce a strong cognate interaction between T cells and B cells. In addition to amplifying the virus-infected B-cell pool, this superantigen-driven interaction leads to the differentiation of virus-specific B cells into plasma cells. Successful interaction between T cells and B cells is required for completion of the viral life cycle.

The intragraft CD8+ T cell response in renal allograft rejection in the mouse

To identify the role of donor class I alloantigens in regulating the CD8+ T cell response to a kidney allograft, we analyzed and compared the CD8+ infiltrate in kidney transplants from MHC class I-deficient (class I-) mouse donors and class I+ controls. One week after transplantation, there was a prominent CD8+ infiltrate in control allografts, whereas CD8+ T cells were virtually absent in grafts from class I- donors. In class I+ allografts, infiltrating CD8+ cells utilized a wide range of T cell receptor (TCR) Vbeta families and their Vbeta usage was similar to that of the systemic CD8+ population. However, there was a modest but significant overrepresentation of cells bearing Vbeta8 in the graft compared with the spleen due to an expansion of CD8+ Vbeta8.3+ cells. This could be detected as early as 1 week and became more pronounced by 3 weeks after transplantation. In 3-week allografts, only 52% of CD8+ cells expressed alphabetaTCR. Among T cells isolated from class I+ grafts, the CD8+ Vbeta8+ cells demonstrated allospecific responses that were numerically larger than responses of the CD8+ Vbeta8- population. In contrast to the early (1 week) time point, significant numbers of CD8+ cells could be isolated from class I- grafts by 3 weeks after transplantation and their Vbeta repertoire resembled that seen in controls. While increasing numbers of CD8+ Vbeta8+ were present in the class I- grafts at 3 weeks, this increase was not statistically significant. Thus, expression of class I alloantigens on a kidney graft plays an important role in regulating the rate of accumulation of CD8+ T cells in rejecting kidney grafts. However, the TCR Vbeta repertoire of the CD8+ T cell infiltrate is largely determined by factors that are independent of normal class I expression on the graft.

Role of the T cell receptor alpha-chain in superantigen recognition

Superantigens bind to antigen-presenting cells on the outside of the major histocompatibility complex (MHC) class II molecule and to T cells via the external face of the T cell receptor (TCR) V beta element. As a consequence, superantigens stimulate populations of T cells in a V beta-specific, non-MHC-restricted manner. However, accumulating evidence has shown an additional contribution of the TCR alpha-chain and polymorphic residues of the MHC molecule to superantigen recognition by some T cells. These data suggest that the TCR and MHC come into contact during superantigen engagement and indirectly modulate the superantigen reactivity. Thus, additional interactions between non-V beta elements of the TCR and MHC play a role in the overall stability of the superantigen/MHC/TCR complex, explaining the influence of the TCR alpha-chain. It is likely that this additional interaction is of greater consequence for weakly reactive T cells. This modulation of superantigen reactivity in individual T cells may have physiological consequences, for example, in the induction of autoimmunity.

Antigen compartmentation and T helper cell tolerance induction

The process of antigen recognition depends in part on the amount of peptide antigen available and the affinity of the T cell receptor for a particular peptide-major histocompatibility complex (MHC) molecule complex. The availability of self antigen is limited by antigen processing, which is compartmentalized such that peptide antigens presented by MHC class I molecules originate in the cytoplasm, whereas peptide antigens presented by MHC class II molecules are acquired from the endocytic pathway. This segregation of the antigen-processing pathways may limit the diversity of antigens that influence the development and selection of, e.g., CD4-positive, MHC class II-specific T cells. Selection in this case might involve only a subset of self-encoded proteins, specifically those that are plasma membrane bound or secreted. To study these aspects of immune development, we engineered pigeon cytochrome for expression in transgenic mice in two forms: one in which it was expressed as a type II plasma membrane protein, and a second in which it was targeted to the mitochondria after cytoplasmic synthesis. Experiments with these mice clearly show that tolerance is induced in the thymus, irrespective of antigen compartmentation. Using radiation bone marrow chimeras, we further show that cytoplasmic/mitochondrial antigen gains access to the MHC class II pathway by direct presentation. As a result of studying the anatomy of the thymus, we show that the amount of antigen and the affinity of the TCR affect the location and time point of thymocytes under-going apoptosis.

Enumeration and characterization of memory cells in the TH compartment

There is a great deal of interest in understanding how helper T cells differentiate in vivo and exert their regulatory role on a developing, immune response. Essential to development of protective immunity is the development of memory T cells. To study memory T cells in vivo we first need the means to identify and characterize these cells as they develop in their complex microenvironments. We have developed a method which allows us to directly purify both primary and memory helper T cells from the draining lymph nodes of mice as they respond to pigeon cytochrome c in vivo. Junctional sequences from these populations and from individual T cells show a strong selection for CDR3 length and residues characteristic of antigen binding. Overall these studies support a model of progressive clonal maturation with the memory T cell repertoire being more homogeneous than that of the primary response. There is some suggestion that affinity maturation may take place after repeated immunization, but on a more modest scale than that seen for antibodies. Finally we present the use of two new technologies that promise to greatly expand the analysis of immune responses in vivo. The use of flow cytometry with simultaneous detection of five and six fluorescence parameters helps to reliably resolve rare subsets of antigen-specific cells in order to understand the progression of their differentiation in vivo. Lastly, we have developed peptide/MHC tetramers as a new class of staining reagent that has wide applicability in the study of T cell responses in vivo.

A one step PCR procedure for analysis of tumor specific T lymphocyte responses

In an effort to develop optimal conditions for analysis of tumor specific T lymphocyte responses, we have studied the effect of changes in the concentration of oligonucleotide primers on the synthesis of TCR cDNAs in one step PCR procedure using Vbeta10 gene subfamily as a model. It was found that synthesis of the TCR cDNAs increases in a roughly linear fashion at primer concentrations between 0.005-0.05 muM. Evaluation of the use of low concentration (0.005 muM) of primers showed these conditions to be adequate for the analysis of TCR Vbeta subfamilies in the spleen of BALB/c mice, but not in the peritoneal exudate cells (PECs), the latter requiring ten-fold higher concentrations of the variable region primers to compensate for the overall low frequency of T lymphocytes in the PECs in comparison to the spleen. Use of these optimal conditions to detect L1210 tumor specific T lymphocyte responses showed that, in the immunized mice, L1210 specific T lymphocyte responses are detectable in the PECs, but not in the spleen cells from these mice. Thus, upon i.p. immunization of DBA/2 mice with irradiated L1210 lymphoma cells, followed by analysis of the PECs by RT/PCR, three TCR Vbeta subfamilies, including Vbeta8.2, Vbeta15 and Vbeta16 were found to contain specific major TCR cDNA bands. The approach described here is very efficient, as it uses a small amount of the 32P isotope (0.5 muCi) followed by direct analysis of the PCR products on a denaturing acrylamide/urea gel. Furthermore, data is also presented that shows that quantitative differences in the levels of individual TCR cDNAs in a particular Vbeta subfamily are preserved during PCR amplification.

Balancing immunity and tolerance: deleting and tuning lymphocyte repertoires

Immunological self-tolerance is ensured by eliminating or inhibiting self-reactive lymphocyte clones, creating physical or functional holes in the B- and T-lymphocyte antigen receptor repertoires. The nature and size of these gaps in our immune defenses must be balanced against the necessity of mounting rapid immune responses to an everchanging array of foreign pathogens. To achieve this balance, only a fraction of particularly hazardous self-reactive clones appears to be physically eliminated from the repertoire in a manner that fully prevents their recruitment into an antimicrobial immune response. Many self-reactive cells are retained with a variety of conditional and potentially flexible restraints: (i) their ability to be triggered by antigen is diminished by mechanisms that tune down signaling by their antigen receptors, (ii) their ability to carry out inflammatory effector functions can be inhibited, and (iii) their capacity to migrate and persist is constrained. This balance between tolerance and immunity can be shifted, altering susceptibility to autoimmune disease and to infection by genetic or environmental differences either in the way antigens are presented, in the tuning molecules that adjust triggering set points for lymphocyte responses to antigen, or in the effector molecules that eliminate, retain, or expand particular clones.

Derivation of T-cell receptor alpha-chain double expresser lines from normal murine mature T cells

Because the T-cell receptor (TCR) alpha-chain locus is known to lack allelic exclusion of rearrangements, and as a recent report revealed the existence of alpha-chain double expressers among normal human peripheral blood lymphocytes (PBL), the possible existence of TCR alpha-chain double expressers among mature murine T cells was examined. Although two-colour staining analysis of normal T-cell populations did not immediately reveal recognizable clusters of V alpha double expressers, alternative in vitro stimulations of normal murine T cells with antibodies to two different TCR V alpha chains reproducibly induced TCR alpha-chain double-expresser lines. TCR complexes with different alpha-chains on such T cells were both shown to be functional. The cell lines were heterogeneous with respect to V beta usage and the ratio of the expressed amounts of the two alpha-chains on the surface. The ratio of the two expressed alpha-chains was found to be very stable over a long period of time. These results are consistent with the earlier report on alpha-chain double expressers among human T cells and also show normal occurrence of TCR alpha-chain double expressers in murine T-cell populations.

B cells are not essential for peripheral T-cell tolerance

Some self-reactive T cells avoid thymic tolerance and become mature peripheral cells. Nevertheless, these cells do not usually attack their hosts because T cells can be inactivated or killed, even after they are mature, by various means. The details of these processes are not fully understood; however, a number of experiments have suggested that peripheral tolerance may be induced in mature mouse T cells by exposure to antigen on resting B cells, cells that can express antigen bound to major histocompatibility complex proteins but that lack critical costimulatory molecules such as B7-1 and B7-2. Conversely, previous experiments have indicated that mature T cells can be stimulated by exposure to antigen on cells such as dendritic cells, cells that are thought to express the essential costimulatory molecules. We tested this idea in vivo by using mice that lack B cells. Unexpectedly, T-cell tolerance and antigen-induced T-cell death occurred normally in mice free of B cells. On the other hand, antigen-specific T-cell expansion in the spleens of such mice was impaired. Finally, we have recently shown that T-cell death in mice can be prevented by exposure to antigen and an inflammatory agent such as bacterial lipopolysaccharide. This was also true in mice that lacked B cells. Overall, these data show that mature T cells can be tolerized and rescued from tolerance in the absence of B cells.

Bcl-2 and Fas/APO-1 regulate distinct pathways to lymphocyte apoptosis

Activation of the cell surface receptor Fas/APO-1 (CD95) induces apoptosis in lymphocytes and regulates immune responses. The cytoplasmic membrane protein Bcl-2 inhibits lymphocyte killing by diverse cytotoxic agents, but we found it provided little protection against Fas/APO-1-transduced apoptosis in B lymphoid cell lines, thymocytes and activated T cells. In contrast, the cowpox virus protease inhibitor CrmA blocked Fas/APO-1-transduced apoptosis, but did not affect cell death induced by gamma-radiation or serum deprivation. Signalling through Fas/APO-1 did not down-regulate Bcl-2 or induce its antagonists Bax and Bcl-xS. In Fas/APO-1-deficient lpr mice, Bcl-2 transgenes markedly augmented the survival of antigen-activated T cells and the abnormal accumulation of lymphocytes (although they did not interfere with deletion of auto-reactive cells in the thymus). These data raise the possibility that Bcl-2 and Fas/APO-1 regulate distinct pathways to lymphocyte apoptosis.

Prophylactic intervention in radiation-leukemia-virus-induced murine lymphoma by the biological response modifier polysaccharide K

Polysaccharide K (PSK) is a biological response modifier used for adjuvant immunotherapy of malignant diseases. We studied the potential applicability of PSK for preventing tumor progression using an experimental model of murine lymphoma. Mice inoculated with the radiation leukemia virus (RadLV) develop thymic lymphomas after a latency of 3-6 months. However, 2 weeks after virus inoculation, prelymphoma cells can already be detected in the thymus. We found that PSK treatment induced hyperresponsiveness to concanavalin A and heightened production of interleukin-2 (IL-2) and IL-4 in spleen cells of both control and prelymphoma mice. The response was transient and was accompanied with a dominant usage of T cells expressing V beta 8, but other T cell subsets were also stimulated by PSK. T lymphoma cells expressing V beta 8.2 underwent apoptosis when incubated with PSK. Treatment of RadLV-inoculated mice with PSK delayed the onset of overt lymphoma (and mortality) but could not protect the mice from the disease. Combined treatment with PSK and a RadLV-specific immunotoxin prevented synergistically the progression of the prelymphoma cells to frank lymphoma. The results suggest that PSK contains a superantigen-like component that selectively activates V beta 8+ T cells. Its administration prelymphoma mice interfered with the process of lymphoma progression.

The T cell antigen receptor beta chain interacts with the extracellular domain of CD3-gamma

Selective pairwise interactions between a number of CD3 chains and the clonotypic T cell antigen receptor (TCR-alpha, -beta) chains have recently been reported. What still remains unanswered is the site of interaction between TCR-beta and CD3-gamma chains. To examine the region of interaction between TCR-beta and CD3-gamma chains, a variety of genetically altered TCR-beta and CD3-gamma chains were constructed using recombinant cDNA techniques. Non-T cells (COS-7) were transfected with cDNA constructs, metabolically labelled, and immunoprecipitates were analysed for assembly using non-equilibrium pH gel electrophoresis (NEPHGE)/SDS-PAGE. The results demonstrated that assembly between TCR-beta and CD3-gamma chains was localized to their extracellular domain. These findings, when coupled with the information on pairwise interactions and formation of higher order subcomplexes, extend our model of the structure of the TCR complex.

Chromophore-assisted laser inactivation of subunits of the T-cell receptor in living cells is spatially restricted

Chromophore-assisted laser inactivation (CALI) is a molecular photoablation technique that has been used to elucidate the in vivo roles of specific proteins in neural development. The interpretation of its effects on proteins in living cells relies on knowing how spatially restricted the CALI-induced damage is in vivo. To determine the spatial specificity of CALI in living cells, we have applied CALI to individual subunits of the T-cell receptor (TCR) complex on the surface of 2B4 hybridoma cells in culture and have examined the consequent structural and functional integrity of the TCR-alpha, TCR-beta and CD3-epsilon. The CALI of TCR-beta resulted in the disruption of the beta subunit and also resulted in a small effect on antibody binding alone to the neighboring TCR-alpha but caused no effect on another subunit, CD3-epsilon. Reciprocal experiments directing CALI to TCR-alpha and CD3-epsilon gave consistent results. No effects other than a simple loss of function were observed for any of these CALI experiments. These data demonstrate the extent of CALI-induced damage within a multisubunit complex in living cells and provide greater confidence for the future application of this technique to understanding in vivo function of proteins during complex cellular processes.

A single retroviral gag precursor signal peptide recognized by FBL-3 tumor-specific cytotoxic T lymphocytes

Several dominant T-cell receptors of cytotoxic T-lymphocyte (CTL) clones specific for FBL-3 tumor antigen were clonally amplified in mixed lymphocyte tumor cell cultures derived from an individual immune mouse. Every CTL clone analyzed had a common specificity for a single epitope in the precursor to cell membrane-associated nonstructural gag-encoded protein, Pr75gag, which can be minimally identified by nine amino acid residues, SIVLCCLCL. This epitope is located within the hydrophobic signal sequence motif that mediates translocation of the protein into the endoplasmic reticulum. These novel observations suggest that expression of Pr75gag in FBL-3 tumor cells led to the amplification of CTLs which recognize the signal sequence of the nonstructural gag-encoded glycoprotein precursor.

The use of mammary tumor virus (Mtv)-negative and single-Mtv mice to evaluate the effects of endogenous viral superantigens on the T cell repertoire

Most laboratory strains of mice have between two and eight endogenous superantigens. These viral superantigens (vSAGs) are coded by genes in the 3' long terminal repeats of endogenous mammary tumor viruses (Mtv's). A line of Mtv-negative mice and several lines of mice containing single Mtv's were created by inbreeding the F2 progeny of CBA/CaJ and C58/J mice, which have no Mtv integrants in common. This allowed the T cell repertoire of H-2k mice, unaffected by Mtv superantigens, as well as the effects of vSAGs upon that repertoire, to be studied. Although each individual mouse had a different mix of C58/J and CBA/CaJ background genes, the T cell repertoires of different Mtv-negative mice were very similar and were reproducible. Since the background genes did not affect the V beta repertoire, there are no super-antigens, other than those encoded by Mtv's, that differ between CBA/CaJ and C58/J. CD4 and CD8 T cells had quite different repertoires in the Mtv-negative mice because of the effects of class I and class II major histocompatibility complex molecules on positive and negative selection. vSAG3 was found to delete V beta 5 T cells, while vSAG8 deleted V beta 7 T cells, and vSAG9 deleted V beta 13 T cells in addition to their previously reported specificities. vSAG17 deletes a small proportion of CD4+ T cells bearing V beta 11 and -12. vSAG14 and -30 have little effect on the T cell repertoire and are not expressed in thymocytes and splenocytes. An endogenous superantigen that has a low avidity for a particular V beta may positively select thymocytes, leading to an increased frequency of peripheral T cells bearing the relevant V beta s. We found evidence that vSAG11 may positively select T cells bearing V beta 8.2. Our data, which analyzed the effects of seven endogenous Mtv's, showed little evidence of positive selection by any other vSAGs on T cells bearing any V beta tested, despite published reports to the contrary.

Allelic exclusion of mouse T cell receptor alpha chains occurs at the time of thymocyte TCR up-regulation

We report a detailed analysis of TCR V alpha and V beta chain expression on immature versus mature thymocytes of normal, TCR beta-transgenic, and TCR alpha-hemizygous mice. Chain pairing between TCR V alpha and V beta chains is random on immature thymocytes, but individual chain pairs are selected in mature thymocytes. This indicates that V alpha-V beta chain pairing preferences are determined during thymic selection, and not as a result of structural constraints. Dual V alpha chain expression is found frequently on immature, but not mature thymocytes. It is not found in TCR alpha-hemizygous mice, showing that cell surface expression of dual alpha chains is caused by lack of allelic exclusion in immature thymocytes. Down-regulation of one of the alpha chains occurs concurrently with differentiation from TCRlo, CD69- to TCRhi, CD69+ phenotype, suggesting that it is associated with positive selection of the functional TCR.

Analysis of T-cell antigen receptor variable region gene usage in patients with thyroid-related pretibial dermopathy

It is unknown whether T cells infiltrating the pretibial skin of patients with thyroid-related pretibial dermopathy represent a primary immune response or participate in a nonspecific inflammatory process. To characterize these T cells at the molecular level, we examined the T-cell antigen receptor variable region gene usage in pretibial skin biopsy specimens obtained from patients with early and late stages of pretibial dermopathy and from individuals with unrelated inflammatory conditions of the pretibial skin. RNA extracted from pretibial biopsy specimens and peripheral blood lymphocytes was reverse transcribed and amplified with the polymerase chain reaction and 22 V alpha and 23 V beta gene-specific oligonucleotide primers. The resulting T-cell receptor (TcR) V alpha and V beta transcripts were verified by Southern hybridization analysis using TcR C-region-specific, digoxigenin-labeled oligonucleotide probes. Compared with matched peripheral blood lymphocytes, the pretibial TcR V alpha and V beta gene repertoire expressed was heterogeneous but revealed marked restriction of V alpha and V beta gene usage in samples derived from patients with active inflammatory pretibial dermopathy of recent onset. In contrast, greater diversity of the TcR V alpha gene repertoire and loss of TcR V beta gene restriction were noted in patients with long-standing, clinically inactive pretibial dermopathy. TcR V gene usage in pretibial tissue and peripheral blood lymphocyte samples obtained from control subjects was unrestricted. Limited variability of TcR V gene usage in early pretibial dermopathy may reflect a primary immune response of antigen-specific T lymphocytes infiltrating the pretibial skin in thyroid-related pretibial dermopathy.

T cell-dependent antibody response to staphylococcal enterotoxin B

Treatment of mice with staphylococcal enterotoxin B (SEB) induces specific T-cell tolerance to this superantigen, characterized by partial deletion of V beta 8+ T cells in vivo and T cell anergy in vitro. In this study we examined the humoral response to SEB in BALB/c mice. Immunization of mice with SEB results in a detectable anti-SEB antibody response. Upon further treatment of mice with SEB, specific antibody levels increase significantly and the response is accelerated--characteristics of a secondary humoral response. The secondary antibody response is T cell dependent, can be transferred to T cell deficient mice with splenocytes and is composed mainly of IgM, IgG1 and IgG2b isotypes, suggesting that Th2 cells provide B cell help in this response. These data demonstrate that at the same time as inducing in vitro unresponsiveness, SEB primes SEB-specific T helper cells to provide help for B cells in a secondary antibody response.

Quantitation of endogenous mouse mammary tumor virus superantigen expression by lymphocyte subsets

Superantigens (SAg) encoded by endogenous mouse mammary tumor viruses (Mtv) interact with the V beta domain of the T cell receptor (TcR-V beta). Presentation of Mtv SAg can lead to stimulation and/or deletion of the reactive T cells, but little is known about the quantitative aspects of SAg presentation. Although monoclonal antibodies have been raised against Mtv SAg, they have not been useful in quantitating SAg protein, which is present in very low amounts in normal cells. Alternative attempts to quantitate Mtv SAg mRNA expression are complicated by the fact that Mtv transcription occurs from multiple loci and in different overlapping reading frames. In this report we describe a novel competitive polymerase chain reaction assay which allows the locus-specific quantitation of SAg expression at the mRNA level in lymphocyte subsets from mouse strains with multiple endogenous Mtv loci. In B cells as well as T cells (CD4+ or CD8+), Mtv-6 SAg is expressed at the highest levels, followed by Mtv-7 SAg and (to a much lesser extent) Mtv-8,9. Consistent with functional Mtv-7 SAg presentation studies, we find that Mtv-7 SAg expression is higher in B cells than in CD8+ T cells and very low in the CD4+ subset. The overall hierarchy in Mtv SAg expression (i.e. Mtv-6 > Mtv-7 > Mtv 8,9) was also observed for mRNA isolated from neonatal thymus. Furthermore, the kinetics of intrathymic deletion of the corresponding TcR-V beta domains during ontogeny correlated with the levels of Mtv SAg expression. Collectively our data suggest that T cell responses to Mtv SAg are largely controlled by SAg expression levels on presenting cells.

Biased T cell receptor V beta gene usage during specific stages of the development of autoimmune sialadenitis in the MRL/lpr mouse model of Sjögren's syndrome

OBJECTIVE

To analyze the repertoire of T cell receptor (TCR) V beta gene transcribed and expressed within the autoimmune lesions of the salivary gland in the MRL/lpr mouse model of Sjögren's syndrome.

METHODS

Monoclonal antibodies (MAb) were used to determine the prevalence of selected V gene elements on T cell infiltrates from salivary glands of MRL/lpr mice. To analyze TCR V beta gene usage, we used reverse-transcriptase polymerase chain reaction (RT-PCR) and single-strand conformational polymorphism (SSCP) analyses.

RESULTS

A predominance of V beta 8+ T cells was detected within the inflammatory lesions during development of autoimmune disease (confirmed by flow cytometry). RT-PCR analysis revealed that in autoimmune sialadenitis, the predominant expression of the V beta 8 gene segment began in the early stages of disease (2-month-old mice) and increased over time. Extensive age-related diversity of TCR V beta gene usage was also observed. SSCP analysis demonstrated a distinct and common binding pattern of the V beta 8 gene PCR product from the cell infiltrates during the course of the disease.

CONCLUSION

Our data suggest that in the MRL/lpr mouse model of Sjögren's syndrome, there is restricted usage of TCR V beta elements according to the stage of the disease, and that V beta 8 are probably used preferentially in the recognition of a single unknown self antigen in the salivary gland.

Multiple binding sites for bacterial superantigens on soluble class II MHC molecules

We used surface plasmon resonance to study the binding of a set of soluble mouse I-E class II major histocompatibility molecules, each occupied by a different single peptide, to the staphylococcal enterotoxin superantigens, SEA and SEB. The rates of association and dissociation to SEA varied greatly depending on the I-E-bound peptide. By contrast, binding to SEB yielded fast association and dissociation rates, which were relatively peptide independent. The results also indicated nonoverlapping binding sites for SEB and SEA on class II and raised the possibility of enhanced SAg presentation to T cells by cross-linking of cell surface class II.

Mechanisms by which the I-ABM12 mutation influences susceptibility to experimental myasthenia gravis: a study in homozygous and heterozygous mice

The I-Abm12 mutation in C57B1/6 (B6) mice yields the B6.C-H-2bm12 (bm12) strain, which is resistant to Experimental Myasthenia Gravis (EMG) induced by immunization with Torpedo acetylcholine receptor (TAChR), while the parental B6 strain is highly susceptible to EMG. CD4+ cells from bm12 mice immunized with TAChR do not recognize three sequence regions of the TAChR alpha subunit which dominate the CD4+ cell sensitization in B6 mice. We immunized with TAChR bm12, B6 and (bm12 x B6)F1 mice. B6 and F1 mice developed EMG with comparable frequency. Their CD4+ cells recognized the same TAChR alpha subunit peptide sequences (T alpha 150-169, T alpha 181-200 and T alpha 360-378). CD4+ cells from TAChR-sensitized F1 mice were challenged with TAChR and alpha subunit epitope peptides, using F1, B6 or bm12 APC. B6 and F1 APC presented all these Ag efficiently, while bm12 APC presented TAChR and peptide T alpha 150-169 poorly and erratically. Anti-TAChR and anti-alpha subunit epitope CD4+ lines propagated from F1 and B6 mice had similar TcR V beta usage. All lines but those specific for the sequence T alpha 150-169 had unrestricted V beta usage. Anti-T alpha 150-169 lines from both B6 and F1 mice had a strong preferential usage of V beta 6. Anti-T alpha 150-169 lines from F1 mice had also a slightly higher V beta 14 usage. B6, bm12 and F1 mice developed similar anti-TAChR Ab titres, and had Ab bound to muscle AChR in comparable amounts. Therefore EMG resistance of bm12 mice must be due to a subtle shift in the anti-AChR Ab repertoire, and absence of special Ab able to cause destruction and/or dysfunction of muscle AChR. This is probably related to the absence of CD4+ cells sensitized to epitopes within the sequence T alpha 150-160, consequent to the inability of the I-Abm12 molecule to present this sequence.

A myelin oligodendrocyte glycoprotein peptide induces typical chronic experimental autoimmune encephalomyelitis in H-2b mice: fine specificity and T cell receptor V beta expression of encephalitogenic T cells

A predominant response to myelin oligodendrocyte glycoprotein (MOG) was recently observed in patients with multiple sclerosis (MS). To study the possible pathogenic role of T cell response to MOG in MS, we have investigated the encephalitogenic potential of MOG. Synthetic MOG peptides, pMOG 1-21, 35-55, 67-87, 104-117 and 202-218, representing predicted T cell epitopes, were injected into C57BL/6J and C3H.SW (H-2b) mice. The mice developed significant specific T cell responses to pMOG 1-21, pMOG 35-55 and pMOG 104-117. However, pMOG 35-55 was the only MOG peptide which could induce neurological impairment. The highly reproducible disease was chronic, with ascending paralysis and neuropathology comparable with those observed in experimental autoimmune encephalomyelitis (EAE) induced by myelin basic protein or proteolipid protein, except that in H-2b mice the disease was consistently non-remitting. These features differ markedly from those which we recently observed in PL (H-2u) mice with pMOG 35-55-induced disease. In PL mice, pMOG 35-55-induces atypical chronic relapsing EAE, the expression and progression of which are unpredictable. Hence, in different mouse strains, the same MOG peptide can induce typical EAE characterized by ascending paralysis, or atypical EAE with unpredictable clinical signs. pMOG 35-55-specific T cells from H-2b mice recognized an epitope within amino acids 40-55 of the MOG molecule, and pMOG 40-55-reactive T cell lines were encephalitogenic upon transfer into syngeneic recipients. The encephalitogenic pMOG 35-55-reactive C57BL/6J T cell lines expressed V beta 1, V beta 6, V beta 8, V beta 14 and V beta 15 gene segments, and the pMOG 35-55-reactive C3H.SW T cell lines expressed V beta 1, V beta 2, V beta 6, V beta 8, V beta 10, V beta 14, and V beta 15 gene segments. However, in both mouse strains, the utilization of the V beta 8 gene product was predominant (40-43%). The highly reproducible encephalitogenic activity of pMOG 35-55 strongly suggests a pathogenic role for T cell reactivity to MOG in MS and supports the possibility that MOG may also be a primary target antigen in the disease.