V beta repertoire in rats and implications for endogenous superantigens

Neonatal dexamethasone treatment induces long-lasting changes in T-cell receptor vbeta repertoire in rats

Glucocorticoids are frequently administered for the prevention of chronic lung disease in infants with respiratory distress syndrome. However, neonatal treatment may have consequences for immune functioning in the long-term. Here we demonstrate that neonatal glucocorticoid treatment has long-lasting effects on mRNA expression of several Vbeta genes within the CD4 and CD8 T cell subset in rats. Changes in the peripheral T cell Vbeta repertoire may be a consequence of altered intrathymic selection events in which corticosterone plays an important role. Indeed, here we show that neonatal glucocorticoid treatment affects corticosterone production by thymic epithelial cells during neonatal life. In conclusion, changes in T cell Vbeta repertoire after neonatal glucocorticoid treatment may contribute to altered immune reactivity in later life.

Superantigens: mechanisms by which they may induce, exacerbate and control autoimmune diseases

Superantigens are polypeptide molecules produced by a broad range of infectious microorganisms which elicit excessive and toxic T-cell responses in mammalian hosts. In light of this property and the fact that autoimmune diseases are frequently the sequelae of microbial infections, it has been suggested that superantigens may be etiologic agents of autoreactive immunological responses resulting in initiation, exacerbation or relapse of autoimmune diseases. This article relates the biology of superantigens to possible mechanisms by which they may exert these activities and reviews the evidence for their roles in various human and animal models of autoimmune disease. Finally, a mechanism of active suppression by superantigen-activated CD4+ T-cells that could be exploited for therapy as well as prophylaxis of human autoimmune diseases is proposed.

T cell response in xenorecognition and xenografts: a review

Xenotransplantation has recently become a subject of interest for the transplantation community due to the current organ shortage, which could be partially or even totally solved by the development of this strategy. The humoral response, which arises as a result of species disparities, is the major obstacle to the success of xenotransplantation. However, if the use of different strategies such as plasmapheresis, immunoadsorption, the utilization of organs from transgenic pigs for complement regulatory molecules and new immunosuppressive drugs, may allow to overcome or reduce the early antibody mediated rejections (hyperacute or acute vascular rejection), delayed responses based on cellular activations will still occur. In this review, despite the fact that different cell populations have been shown to be implicated in these phenomena (NK, granulocytes, macrophages), we will focus on recent published information concerning T cell response only, in xenorecognition.

T Cell Repertoire Alterations of Vascularized Xenografts

The role of T cells in the rejection of vascularized xenografts has been little explored. Because of the high potential diversity of xenoantigens, it has been suggested that xenotransplantation could induce a strong cellular response that could contribute to delayed rejection. Alternatively, alterations in molecular interactions could impair the T cell response. Because the analysis of TCR repertoire in vivo indirectly reflects the nature and the magnitude of T cell xenorecognition, we took advantage of the possibility of obtaining long term survival of hamster heart xenografts in rat recipients treated with a combination of cobra venom factor and cyclosporin A (CsA), to analyze T cell infiltration and, for the first time, Vβ TCR usage, at the complementarity-determining region 3 level, in accommodated and rejected xenografts, compared with allografts. After withdrawal of CsA (on day 40), the analysis of Vβ family expression and corresponding complementarity-determining region 3 lengths in rejected xenografts revealed a Gaussian pattern, in contrast to a much more restricted pattern in rejected allografts (p = 0.002), suggesting that, after withdrawal of CsA, all the underrepresented T cell clones are rapidly expanded in xenografts. These results correlate with the rapid kinetics of rejection (4 ± 1 days), the high number of T cells, the rapid expression of markers of activation (IL-2 receptor α-chain and class II receptor), and the strong deposit of IgG Abs in rejected xenografts. Taken together, these results suggest that the intensity and diversity of the T cell response to xenografts could be stronger than the response to allografts in vivo.

Differential CD4/CD8 subset-specific expression of highly homologous rat Tcrb-V8 family members suggests a role of CDR2 and/or CDR4 (HV4) in MHC class-specific thymic selection

Different rat Tcrb haplotypes express either TCR beta variable segment (Tcrb-V) 8.2l or 8.4a. Both V segments bind the mAb R78 but differ by one conservative substitution (L14V) and clusters of two and four substitutions in the complementarity-determining region (CDR) 2 and CDR4 [hypervariable loop 4 (HV4)]. Independently of MHC alleles numbers of R78+ CD4+ cells are lower in Tcrb-V8.2l-expressing than in Tcrb-V8.4a-expressing strains. Expression of R78+ TCR during T cell development, analysis of backcross populations and generation of a Tcrb congenic strain [LEW.TCRB(AS)] define two mechanisms how Tcrb haplotypes affect the frequency of R78+ cells, one acting prior to thymic selection leading to up to 2-fold higher frequency of Tcrb-V8.4a versus Tcrb-V8.2l in unselected thymocytes and another occurring between the TCRlow and the CD4/CD8 single-positive stage. The latter leads to a 50% reduction of frequency of Tcrb-V8.4a CD8+ cells but not CD4+ cells and does not affect either subset of Tcrb-V8.2l cells. A comparison of rat classical class I MHC (RT1.A) sequences and current models of TCR-MHC-peptide interaction suggests that this reduction in frequency of Tcrb-V8.4a CD8 cells may be a consequence of differential selection of Tcrb-V8.2l versus Tcrb-V8.4a TCR by differential binding of CDR2beta to highly conserved areas of C-terminal parts of the alpha helices of class I MHC molecules.

Molecular and Genetic Requirements for Preferential Recruitment of TCRBV8S2+ T Cells in Lewis Rat Experimental Autoimmune Encephalomyelitis

The underlying mechanisms behind the preferential expression of select TCRBV products in certain autoimmune illnesses, such as multiple sclerosis and some models of experimental autoimmune encephalomyelitis (EAE), have principally remained enigmatic. In this study, we examined the mutual role of nonself- vs self-origin of antigenic myelin basic protein (MBP) peptides and given MHC haplotypes in relation to the relative frequency of activated TCRBV8S2+ T lymphocytes in the Lewis (LEW) rat EAE model. Inbred MHC (RT1) congenic LEW rats (LEW (RT1l), LEW.1AV1 (RT1av1), and LEW.1W (RT1u)) were immunized with the 63 to 88 peptide of the guinea pig MBP (MBPGP63-88). Additionally, LEW rats were immunized with the corresponding autologous rat sequence (MBPRAT63-88). Although EAE ensued in all MBP peptide/LEW rat strain combinations, only LEW rats immunized with the heterologous MBPGP63-88 peptide elicited T cell responses encompassing a bias toward TCRBV8S2 expression, as determined by flow cytometric analyses. Reduction of TCRBV8S2+ T cells led to mitigation of disease severity in LEW rats immunized with MBPGP63-88, but not with MBPRAT63-88, indicating that critical encephalitogenic characteristics are associated with this T cell subset. We conclude that the preferential recruitment of TCRBV8S2+ T cells in the LEW rat EAE model is due to selective, high-avidity recognition of the nonself-MBPGP63-88 in the context of the RT1.Bl molecule. This inference lends support to the notion that the highly restricted TCR repertoire of the self-MBP-reactive T cells in certain genetically predisposed multiple sclerosis patients may have its source in a multistep molecular mimicry event.

Quantitative assessment of myelin basic protein-reactive T cell entry to the central nervous system by using oligonucleotide probes complementary to VDJ junctional sequences of rat TCR beta-chain

The VDJ junctional region represents the most diverse part of the antigenic TCR. We have previously reported that of 200 sequenced TCR beta-chains of rat MBP-reactive T cells, rarely did two share sequence homology over the entire CDR3 region. In this study, we demonstrate that sequences of the TCR CDR3 region are excellent clonotypic markers for rat MBP-reactive T cell clones and oligonucleotide probes complementary to the CDR3 region of three T cell clones specifically recognized the TCR from which they were derived, but failed to recognize syngeneic T cells that express a similar TCR beta-chain or T cells that share both V beta and J beta usage. To explore this observation, we determined the ability of MBP-reactive T cell clones to enter the CNS. We were able to show that some MBP-reactive T cell clones have an augmented ability to enter the CNS and that fully-activated T cells have a higher penetrating activity than their less-activated T cell counterparts.

Immunobiology and immunotherapeutic implications of syngeneic/autologous graft-versus-host disease

Administration of the immunosuppressive drug cyclosporine (CsA) after syngeneic/autologous bone marrow transplantation (BMT) elicits an autoimmune syndrome with pathology virtually identical to graft-vs-host disease (GVHD). The induction of this syndrome, termed syngeneic/autologous GVHD, is a two-tiered process requiring both the active inhibition of thymic-dependent clonal deletion and the elimination of mature T cells that have an immunoregulatory effect. Eradication of the peripheral immunoregulatory compartment by the preparative regimen provides a permissive environment for the activation of the syngeneic/autologous GVHD effector T cells. Although the repertoire of autoreactive effector T lymphocytes is highly conserved, these T cells promiscuously recognize MHC class II determinants. This novel specificity of the autoreactive lymphocytes appears to be dependent on the peptide derived from the MHC class II invariant chain. Recent studies also suggest that these promiscuous autoreactive T cells can effectively target and eliminate MHC class II-expressing tumor cells. Administration of cytokines that upregulate the target antigen or expand the effector population can potentiate the antitumor activity of syngeneic/autologous GVHD. Although the induction of syngeneic/autologous GVHD is an untoward effect of CsA immunosuppression, mobilization of these autoimmune mechanisms provides a promising immunotherapeutic approach for certain neoplastic diseases.

The lesions of cyclosporine-induced autoimmune disease can be equally well elicited by CD4 or CD8 effector T cells

Lethally irradiated Lewis rats reconstituted with syngeneic bone marrow and given cyclosporine for 4 weeks develop a graft-versus-host-like disease upon withdrawal of CsA. Autoreactive T cells inducing this thymus-dependent autoimmune disease, termed CsA-AI, are demonstrable by adoptive transfer, provided regulatory cells in recipient rats are eliminated. Earlier studies have not unequivocally defined the effector T cells responsible for development of CsA-AI. Some of these studies suggest that both CD4 and CD8 T cells are required, while other studies indicate disease transfer by CD4 or CD8 T cells only. To further clarify this issue, it was necessary to study putative effector T cells in a well-defined setting. Hence, adoptive transfer studies were designed wherein the effect of the T cells of interest could be studied without being influenced by T cells of unwanted origin. Accordingly, recipient rats were thymectomized prior to irradiation, lymph node cells (LNC) from diseased donor rats were depleted of CD4 or CD8 cells before adoptive transfer, and recipients were treated in vivo with CD4- or CD8-depleting mAb. The results showed that CsA-AI developed after adoptive transfer with LNC depleted of either CD4 or CD8 cells. Analysis of PBL and of histologic specimens confirmed the absence of the depleted subset. In both instances, the typical MHC class II expression on keratinocytes and the presence of ED1+ macrophages were identical to the lesions in the primary donors, where both CD4 and CD8 T cells were present. Analysis of the T cell Receptor beta-chain variable region repertoires revealed that their expression patterns in LNC of diseased donors or recipients was comparable to that in normal thymus or LNC--hence, there was no restricted BV repertoire. Taken in toto, our observations indicate that CsA-AI involves both CD4 and CD8 T cells, and that these subsets can generate identical macroscopic and microscopic signs of disease.

Effect of in vivo rapamycin treatment on de novo T-cell development in relation to induction of autoimmune-like immunopathology in the rat

Cyclosporine (CsA) and FK506 are structurally unrelated immunosuppressants, but function in similar ways. FK506 and rapamycin (RAPA), on the other hand, have structural similarities, but act by different mechanisms to yield immunosuppression. Besides their immunosuppressive action, CsA and FK506 are known to interfere with T-cell development. CsA treatment after lethal X-irradiation and syngeneic bone marrow transplantation results in autoimmune disease, which is referred to as CsA-induced autoimmunity. In this study, we examined the effect of RAPA on T-cell development by flow cytometry and immunohistochemistry in female Lewis and Brown Norway rats. Irradiation and syngeneic bone marrow transplantation were performed before a 4-week course of RAPA administration to determine de novo T-cell development in relation to possible autoimmune phenomena. RAPA interfered with the maturation of thymocytes to the CD4+CD8+ DP stage, which resulted in a relative increase in TCRalphabeta(-) immature thymocytes, localized in a rim along the outer cortex. The thymus of RAPA-treated animals had a thinner cortex, leading to stronger thymic atrophy. In the periphery, only a few T cells were observed at the end of RAPA treatment. In the Lewis rat, a normal CD4/CD8 T-cell ratio and an increased Th1/Th2 ratio was observed within the T-cell population. Six weeks after cessation of RAPA therapy, the T-cell compartment was restored to normal, with respect to number and phenotype. In Brown Norway rats, however, T-cell areas were barely detectable at the end of RAPA treatment. The CD4/CD8 T-cell ratio was decreased as a result of a lower number of CD4 T cells; the Th1/Th2 ratio was increased but Th2 remained higher. Similar to Lewis rats, the situation was almost normalized 6 weeks after cessation of RAPA administration. However, Brown Norway rats, in contrast to Lewis rats, showed T-cell infiltration and concomitant induction of MHC class II in the submandibular salivary gland, as well as insulitis, in the pancreas. Possible relationships to Sjogren's disease and diabetes remain to be established.

Resistance to tolerance induction in the diabetes-prone biobreeding rat as one manifestation of abnormal responses to superantigens

T cells taken from normal rats treated with an exogenous source of bacterial superantigen in vivo specifically failed to proliferate following re-stimulation with the same superantigen in vitro. Responsiveness was restored following the addition of an exogenous source of interleukin-2 indicating that the T cells had been made functionally tolerant and not deleted. While staphylococcal enterotoxin treatment of normal rats virtually abolished T-cell proliferation to the same enterotoxin in vitro, T cells from similarly treated diabetes-prone Biobreeding (BB-DP) rats were markedly resistant to this in vivo effect. Responses in BB-DP rats were never reduced by more than 50% even when a 4 times more effective dose of enterotoxin was employed. The resistance of BB-DP peripheral T cells to staphylococcal enterotoxin-induced tolerance could not be attributed to differences in T-cell receptor V beta chain family usage of BB-DP vs normal T cells but was associated with qualitative differences in the way in which BB-DP T cells responded to staphylococcal enterotoxins in vitro. While under optimal stimulatory conditions BB-DP T-cell proliferative responses to staphylococcal enterotoxins appeared comparable to those from non-diabetes-prone animals, under superoptimal conditions BB-DP, but not diabetes-resistant, donor T-cell proliferative responses to staphylococcal enterotoxins could be blocked in vitro with antibodies to CD4 antigens. In addition, BB-DP T-cell proliferative responses were more sensitive to suboptimal staphylococcal enterotoxin doses in vitro. We discuss ways in which abnormal BB-DP T-cell responses to superantigens in general and resistance to staphylococcal enterotoxin-mediated tolerance induction in particular may play a role in the generation of a peripheral T-cell repertoire prone to autoimmunity.

Enhanced HIV-1 replication in V beta 12 T cells due to human cytomegalovirus in monocytes: evidence for a putative herpesvirus superantigen

HIV-1 replicates more efficiently in cultured IL-2-dependent CD4 T cells expressing V beta 12 T cell receptors (TCRs) rather than other TCRs (Laurence et al., 1992). A viral reservoir is frequently established in V beta 12 T cells in HIV-1-infected patients. Here we show that cytomegalovirus (CMV) is responsible for V beta 12-selective HIV-1 replication that is indistinguishable from the effect of known superantigens (SAGs). This effect is dependent on direct contact of T cells with CMV-infected monocytes. CMV infection, but not ie1 or ie2 transfection, reproduces this effect in a monocytoid cell line (U937). In HIV-infected patients, the presence of CMV antibodies correlates with an HIV-1 viral load preferentially skewed to the V beta 12 subset. Together, these data suggest that a CMV gene product is responsible for a SAG-driven V beta 12-selective HIV-1 reservoir in vivo.

T-cell receptor (TCR) usage in Lewis rat experimental autoimmune encephalomyelitis: TCR beta-chain-variable-region V beta 8.2-positive T cells are not essential for induction and course of disease

Predominant usage of V beta 8.2 gene segments, encoding a T-cell receptor (TCR) beta chain variable region, has been reported for pathogenic Lewis rat T cells reactive to myelin basic protein (MBP). However, up to 75% of the alpha/beta T cells in a panel of MBP-specific T-cell lines did not display TCR V beta 8.2, V beta 8.5, V beta 10, or V beta 16 elements. To further investigate TCR usage, we sorted the T-cell lines for V beta 8.2- and V beta 10-positive T cells or depleted the lines of cells with these TCRs. V beta 8.2-positive T cells and one of the depleted T-cell lines strongly reacted against the MBP peptide MBP-(68-88). The depleted T-cell line caused marked experimental autoimmune encephalomyelitis (EAE) even in Lewis rats in which endogenous V beta 8.2-positive T cells had been eliminated by neonatal treatment with anti-V beta 8.2 monoclonal antibodies. T-cell hybridomas generated from this line predominantly used V beta 3 TCR genes coexpressed with TCR V alpha 2 transcripts, which were also used by V beta 8.2-positive T cells. Furthermore, V beta 10-positive T cells reactive to MBP-(44-67) were encephalitogenic when injected immediately after positive selection. After induction of EAE by sorted V beta 8.2- or V beta 10-positive T-cell lines, immunocytochemical analysis of the spinal cord tissue showed a predominance of the injected TCR or of nontypable alpha/beta T cells after injection of the depleted line. Our results demonstrate heterogeneity of TCR beta-chain usage even for a single autoantigen in an inbred strain. Moreover, V beta 8.2-positive T cells are not essential for the induction and progression of adoptive-transfer EAE.

The inflammatory lesion of T cell line transferred experimental autoimmune encephalomyelitis of the Lewis rat: distinct nature of parenchymal and perivascular infiltrates

We have investigated the T cell receptor (TCR) repertoire in the inflammatory infiltrates of T line-transferred experimental autoimmune encephalomyelitis (EAE) of the Lewis rats. Using a panel of TCR V beta-specific monoclonal antibodies (mAbs) and immunocytochemistry, we studied the nature of the T cells entering the central nervous system (CNS) after transfer of either myelin basic protein (MBP)-reactive, or MBP-reactive but non-encephalitogenic T cell lines. All the MBP-specific T cell lines predominantly used the V beta 8.2 TCR chain. T cell lines specific for the tuberculin purified protein derivative (PPD), using TCR V genes different from V beta 8.2, served as controls. We first studied the time course of T cells entering the CNS. In all recipient rats, small, but significant numbers of alpha beta-TCR-expressing infiltrate cells appeared in the CNS within the first 24 h after T cell transfer. In animals injected with either type of MBP-reactive T cells, the early infiltrate cells were preferentially located within the parenchyma of the spinal cord, while in PDD T line-injected rats, the lymphocytes were mostly found in the meninges. TCR V beta gene usage was examined on the peak of clinical disease. Six days after T cell transfer, the TCR repertoire used by infiltrating lymphocytes in general seemed to be highly diverse. None of the V beta isotypes examined (i.e. V beta 8.2, V beta 8.5 or V beta 10) was used by a major population of the alpha beta-TCR-positive T cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat T cell response to superantigens. I. V beta-restricted clonal deletion of rat T cells differentiating in rat-->mouse chimeras

T cells of mice display V beta-specific reactivity for a spectrum of mouse mammary tumor virus (Mtv) antigens; confrontation with these antigens during ontogeny causes substantial "holes" in the T cell repertoire. Since endogenous Mtv antigens are rare in other species, the question arises whether V beta-specific recognition of Mtv antigens is unique to mice. To examine this question, rat T cells were allowed to differentiate from stem cells in severe combined immunodeficiency (SCID) mice. These rat-->mouse xenochimeras were prepared under a variety of conditions. The results show that rat T cells are strongly reactive to mouse Mtv antigens, both in terms of tolerogenicity and immunogenicity. In fact, the V beta specificity of rat and mouse T cells for Mtv antigens is almost indistinguishable.

Preferential distribution of V beta 8.2-positive T cells in the central nervous system of rats with myelin basic protein-induced autoimmune encephalomyelitis

To determine the role of encephalitogenic T cells in the formation of lesions in the central nervous system (CNS), experimental autoimmune encephalomyelitis (EAE) was induced in Lewis rats by immunization with either myelin basic protein (MBP) or the synthetic peptide which corresponds to the 87-100 sequence of guinea pig MBP, and T cells expressing T cell receptor (TcR) V beta 8.2, V beta 8.5, V beta 10 and V beta 16 in the lymphoid organs and CNS were localized and quantified by flow cytometry (FCM) and immunohistochemistry. In normal rats, the percentage of T cells expressing these V beta phenotypes to the total number of TcR alpha beta+ T cells, as determined by FCM, ranged from 5% to 10% in the lymph node. V beta 16+ T cells were the most predominant population among the four V beta subsets tested. Essentially the same findings were obtained from the analysis of the lymphoid organs of rats with EAE which had been induced by immunization with the same two antigens. In sharp contrast, 15-20% of the T cells isolated from lesions of MBP-induced EAE expressed V beta 8.2. Thus, the percentage of V beta 8.2+ T cells in the EAE lesions was threefold higher than that in the lymph node, while the proportions of V beta 8.5+, V beta 10+ and V beta 16+ T cells were about the same in both organs. The predominance of V beta 8.2+ T cells in EAE lesions was confirmed by counts of immunohistochemically stained T cells in the spinal cord. Moreover, it was revealed that (i) the predominance of V beta 8.2+ T cells was greatest during the development of EAE and became less obvious at the recovery state, and (ii) at the peak stage of EAE, approximately 85% of V beta 8.2+ T cells were distributed in the parenchyma while 15% were in the perivascular space of the CNS vessels. These findings indicate that encephalitogenic T cells which express V beta 8.2 infiltrate the CNS at a very early stage of EAE and become the predominant population in infiltrating T cells, and further suggest that encephalitogenic T cells, not only recruit inflammatory cells in the CNS, but also cause neural tissue damage, such as demyelination.

Stimulation of rat spleen cells by staphylococcal enterotoxins

There is much interest in staphylococcal enterotoxins as T cell mitogens in humans, mice and rabbits. Rat spleen cells were shown to proliferate in response to staphylococcal enterotoxins A and B and toxic shock syndrome toxin-1 at concentrations (5 to 500 ng ml-1) which also stimulate mouse spleen cells. The proliferative response to all these enterotoxins was inhibited by cyclosporin A, indicating the response to be predominantly that of T cells. These results indicate that the rat provides another convenient model for the analysis of T cell responses to enterotoxins.

Bacterial superantigens mediate T cell deletions in the mouse severe combined immunodeficiency-human liver/thymus model

The ability to analyze T cell receptor (TCR) thymic repertoire shaping in humans by self and foreign ligands is hampered by the lack of suitable models. We recently documented that the mouse severe combined immunodeficiency (SCID)-human fetal liver/thymus model recapitulates the TCR V beta gene repertoire of human thymocytes. Here, we show that an exogenous superantigen, staphylococcal enterotoxin B, administered to such mice induces clonal deletions in both CD4+8- and CD8+4- cells involving the same human V beta clones that are selected in vitro by this toxin. This model, therefore, may allow comprehensive studies into the effects of microbial and other agents on human T cell thymic selection processes in a biologically relevant setting.