Measuring efficiency of tolerance induced by cortical TSCOT+ TEC

초록

In order to characterize the role of thymic stromal compartments for the tolerance induction for more mechanistic details, we used a mouse model restricting LacZ to thymic stromal cotransporter (TSCOT) expressed in the cortical thymic epithelial cells (TDLacZ). When examining endogenous responses directed against LacZ, we observed significant tolerance. This was evidenced in a diverse T cell repertoire as measured by both a CD4 T cell proliferation assay and an antigen-specific antibody isotype analysis. This tolerance process was at least partially independent of Autoimmune Regulatory Element gene expression. When TDLacZ mice were crossed to a CD4 TCR transgenic (BgII) reactive against LacZ, there was a complete deletion of double positive thymocytes. Fetal thymic reaggregate culture of CD45 and UEA-1 depleted thymic stromal cells from TDLacZ and sorted TCR-bearing thymocytes excluded the possibility of cross presentation by thymic dendritic cells and medullary epithelial cells for the deletion. The thymus of this mouse contains approximately 4,300 TSCOT+ cells, each expressing several thousand molecules of the LacZ antigen. This suggests that single cTEC can handle 10 thousand thymocytes in average to scan for the auto reactive TCR bearing thymocytes in steady state condition. TSCOT+ cells express the cortical marker CDR1, CD40 and CD80, CD54, and MHCII, suggesting efficient antigen presenting function in contrast to the previous notion that cTEC is not good APC. Overall, these results demonstrate that cortical epithelium is not excluded from the negative selection, actively participate with surprising efficiency in tolerance induction, and presence of AIRE independent alternative pathway for the central/tissue specific tolerance.