EVIDENCE FOR A PREFERENTIAL V-BETA USAGE BY THE T-CELLS WHICH ADOPTIVELY TRANSFER DIABETES IN NOD MICE

Non-obese diabetic (NOD) mice become spontaneously diabetic as a result of a genetically programmed autoimmune process mediated by autoreactive T lymphocytes and directed against beta cell antigen(s). Studies dealing with T cell receptor (TcR) variable (V) gene usage by such autoreactive T lymphocytes have given contrasted results. Various reasons may explain these discrepancies: the multiplicity of antigenic epitopes putatively recognized by T cells, the ambiguity between specifically committed T cells and passenger lymphocytes homing randomly to the pancreas, the necessarily limited size of the T cell clone panels which have been analyzed for TcR rearrangements and, last but not least, the flexibility of T cell repertoires. To circumvent some of these difficulties, we have decided to concentrate upon the T cell population present in diseased animals and capable of transferring diabetes into young naive NOD recipients. This population, composed of CD4+ and CD8+ T cells, is presumably committed against the relevant beta cell antigens and is the most likely to reveal a bias in V gene usage if such a bias does indeed exist. To find out whether certain Vbeta genes are more frequently used than others by such pathogenic T cells. T lymphocytes from diabetic donors have been depleted in vitro of defined Vbeta subsets before being reinoculated into permissive recipients. Out of four Vbeta families probed under such conditions, three (Vbeta8, Vbeta5 and Vbeta11) are neutral. Their absence neither increases nor reduces the final incidence of successful transfers, indicating that these gene segments are not preferentially used. In contrast, the depletion of Vbeta6-positive T cells results in a severe reduction of transfers, suggesting that Vbeta6 gene is used with a relatively high frequency by diabetogenic CD4+ and/or CD8+ T cells. To define more precisely which subset uses Vbeta6 gene preferentially, we have performed mixing experiments with deleted and intact subsets. The results, based on disease transfer and insulitis severity, indicate that the Vbeta6 bias affects predominantly the CD4+ subset. Thus, at variance with several studies concluding that V gene usage in NOD mice is heterogeneous, OUT present data suggest that disease transferring T cells use a relatively restricted set of Vbeta genes.