Identification of key amino acids of the mouse mammary tumor virus superantigen involved in the specific interaction with T-cell receptor V(beta) domains

Experimental Arthritis in the Rat Induced by the Superantigen Staphylococcal Enterotoxin A

The pathogenesis of rheumatoid arthritis (RA) is incompletely understood. Human endogenous retroviruses (HERVs) and their superantigenic envelope protein (env) have been implicated in the pathogenesis of RA. In the present investigation, the arthritogenic potential of the superantigen staphylococcal enterotoxin A (SEA) has been investigated. In the present investigation, the bacterial superantigen staphylococcal enterotoxin A (SEA) was injected into the right knee joint of 15 Lewis rats. Further nine animals received saline. Animals were sacrificed one, five and 10 days after the injection, respectively. The antigens CD3, CD4, CD8, MHC class I, MHC class II, Pax5 and CD138 were investigated by immunohistochemistry on cryo-sections. After intra-articular SEA injection, the inflammation was initially dominated by CD8+ T cells. In the course of the investigation, the numbers of CD4+, Pax5+, CD138+ and MHC class II+ cells increased. CD3 was expressed in low numbers as compared to CD8. After saline injection, no similar inflammatory response has been detected. The arthritis induced by the superantigen SEA may be a novel model for inflammatory joint diseases, that is rheumatoid arthritis or juvenile idiopathic arthritis.

Prevalent de novo somatic mutations in superantigen genes of mouse mammary tumor viruses in the genome of C57BL/6J mice and its potential implication in the immune system

Background

Superantigens (SAgs) of mouse mammary tumor viruses (MMTVs) play a crucial role in T cell selection in the thymus in a T cell receptor (TCR) Vβ-specific manner and SAgs presented by B cells activate T cells in the periphery. The peripheral T cell repertoire is dynamically shaped by the steady induction of T cell tolerance against self antigens throughout the lifespan. We hypothesize that de novo somatic mutation of endogenous MMTV SAgs contributes to the modulation of the peripheral T cell repertoire.

Results

SAg coding sequences were cloned from the genomic DNAs and/or cDNAs of various tissues of female C57BL/6J mice. A total of 68 unique SAg sequences (54 translated sequences) were identified from the genomic DNAs of liver, lungs, and bone marrow, which are presumed to harbor only three endogenous MMTV loci (Mtv-8, Mtv-9, and Mtv-17). Similarly, 69 unique SAg sequences (58 translated sequences) were cloned from the cDNAs of 18 different tissues. Examination of putative TCR Vβ specificity suggested that some of the SAg isoforms identified in this study have Vβ specificities different from the reference SAgs of Mtv-8, Mtv-9, or Mtv-17.

Conclusion

The pool of diverse SAg isoforms, generated by de novo somatic mutation, may play a role in the shaping of the peripheral T cell repertoire including the autoimmune T cell population.

Cerebral gene expression of superantigen encephalitis in the lewis rat induced by staphylococcal enterotoxin a

Superantigens were suggested to play a role in the pathogenesis of different autoimmune diseases including multiple sclerosis (MS). Previously, it was demonstrated that local expression of the superantigen, staphylococcal enterotoxin A (SEA) in the brain of rats may lead to encephalitis which was amplified by using intravenous injection of concanavalin A (ConA)-activated splenocytes. In the present investigation, gene expression was studied in the rat brain 8 days after an injection of 50 mul of 1 mg/ml SEA or saline and 5 days after an intravenous injection of 1 x 10(7) ConA-activated spleen cells. Of 8800 genes investigated (Affymetrix, rat genome U34A), the expression of 106 genes was significantly and at least threefold increased with SEA, while the expression of 29 genes was decreased at least threefold. Increased gene expression was compatible with an intracerebral inflammatory response mediated by antigen-presenting cells and CD8+ T lymphocytes. Elevated chemokines comprised RANTES (CCL5), osteopontin, MCP-1 (CCL2) and CXCL10. Further, genes with increased expression were assigned to the extracellular matrix, microglia/macrophage cell elements, astrocytes (GFAP) and phagocytosis. There was considerable conformity between previously reported gene expression profiles for experimental autoimmune encephalomyelitis (EAE) or MS and the present findings. Our data are in line with the concept that T-cell superantigen locally expressed in the central nervous system induces an inflammatory response. Therefore, the study of gene expression profiles does not seem to allow clear conclusions with respect to the aetiology of central nervous system autoimmune diseases.

Signaling by the kinase MINK is essential in the negative selection of autoreactive thymocytes

Signaling through the T cell antigen receptor leading to elimination (negative selection) or differentiation (positive selection) of developing thymocytes generates a self-tolerant T cell repertoire. Here we report that the serine-threonine kinase MINK selectively connects the T cell receptor to a signaling pathway that mediates negative but not positive selection. Analysis of this pathway suggested that the essential function of MINK in the elimination of self-reactive thymocytes may be associated with 'downstream' activation of Jun kinase and enhancement of expression of the proapoptotic molecule Bim.

Differential regulation of peripheral CD4+ T cell tolerance induced by deletion and TCR revision

In Vbeta5 transgenic mice, mature Vbeta5(+)CD4(+) T cells are tolerized upon recognition of a self Ag, encoded by a defective endogenous retrovirus, whose expression is confined to the lymphoid periphery. Cells are driven by the tolerogen to enter one of two tolerance pathways, deletion or TCR revision. CD4(+) T cells entering the former pathway are rendered anergic and then eliminated. In contrast, TCR revision drives gene rearrangement at the endogenous TCR beta locus and results in the appearance of Vbeta5(-), endogenous Vbeta(+), CD4(+) T cells that are both self-tolerant and functional. An analysis of the molecules that influence each of these pathways was conducted to understand better the nature of the interactions that control tolerance induction in the lymphoid periphery. These studies reveal that deletion is efficient in reconstituted radiation chimeras and is B cell, CD28, inducible costimulatory molecule, Fas, CD4, and CD8 independent. In contrast, TCR revision is radiosensitive, B cell, CD28, and inducible costimulatory molecule dependent, Fas and CD4 influenced, and CD8 independent. Our data demonstrate the differential regulation of these two divergent tolerance pathways, despite the fact that they are both driven by the same tolerogen and restricted to mature CD4(+) T cells.

Regions of mouse mammary tumor virus superantigen involved in interaction with the major histocompatibility complex class II I-A molecule

To study the major histocompatibility complex class II I-E dependence of mouse mammary tumor virus (MMTV) superantigens, we constructed hybrids between the I-E-dependent MMTV(GR) and the I-E-independent mtv-7 superantigens and tested them in vivo. Our results suggest that, although the C-terminal third mediates I-A interaction, additional binding sites are located elsewhere in the superantigen.