Klonale Expansion CD4+ T-Zellen bei der autoimmunen Myasthenia gravis

This investigation concerns the analysis of the T cell receptor (TCR) repertoire in autoimmune myasthenia gravis (MG). MG is an autoimmune disease caused by autoantibodies directed against the acetylcholine receptor (AChR) at the neuromuscular junction. Due to frequently associated thymic abnormalities, positive effects of thymectomy on the course of disease and detection of AChR specific T lymphocytes (T cells), CD4 positive T cells are believed to have a key role in MG pathogenesis. However, to date little is known about these T cells´ origin and antigen specificity. The aim of this study is therefore to identify and to characterize potentially pathogenic and myasthenogenic T cells in autoimmune MG. Based on the hypothesis of possibly expanded pathogenic T cell populations in the peripheral blood (PB) of MG patients flow cytometric analyses of T cells from 118 MG patients and 118 healthy controls were performed. In PB from 21 MG patients significantly expanded CD4 positive T cells could be detected (≥ 5 standard deviations above the mean of age and sex matched healthy controls, p<0.001). These CD4 positive T cell expansions corresponded to excessive expression of one or few TCR variable beta chains (BV). Investigating all MG patients T cell expansions on different TCR BV chains could be detected without a disproportionate frequently expansion of any specific TCR BV chain. Thus, these investigations indicate the immunogical pattern of an individual restricted TCR repertoire. In order to provide evidence for a clonal origin of these expanded T cells complementary determining region 3 (CDR3) of the TCR was analyzed, because this region is particularly important for antigen recognition. An antigen-independent single cell cloning technique was performed to generate in vitro T cell clones (TCC). TCC representing the expanded T cell populations could be identified by CDR3 length analysis (spectratyping). Following TCR sequencing of in vitro TCC showed identical CDR3 DNA sequences in 4 of 5 index MG patients. These results prove for the first time clonal CD4 positive T cell expansions in autoimmune MG. Future clarification of the antigen specificity may attribute a relevant role to these clonal expanded T cells in autoimmune MG pathogenesis and thus provide an important contribution in the understanding of this disease.