Mechanisms of T cell tolerance to the RNA-binding nuclear autoantigen human La/SS-B.

摘要

Cellular mechanisms of T cell tolerance to nuclear antigens, especially those that bind RNA, are unclear. Presented here is the first T Cell Receptor (TCR)/neo-self antigen (Ag) double transgenic (Tg) mouse model to investigate CD4+ T cell tolerance to a ubiquitous nuclear ribonucleoprotein. We hypothesized that thymic tolerance to the ubiquitously expressed, human La (hLa)/Sjogren's Syndrome (SS)-B autoantigen occurs and is influenced by antigen presentation.;We generated T cell hybridomas specific for the immunodominant hLa epitope 61-84 and determined that they expressed TCRs with similar characteristics. Individual human CD2 promoter-driven constructs of the alpha and beta chains from one of these TCRs, designated 3B5.8, were coinjected to generate a hLa-specific TCR transgenic mouse. Essentially all (98-99%) peripheral CD4 + T cells from 3B5.8 TCR (Valpha8.4/Vbeta10 I-Ek-restricted TCR) Tg mice were Vbeta10+. Tg Vbeta10 cell surface expression levels were physiologically indistinguishable from that of non-Tg mice. 3B5.8 T cells responded specifically to stimulation with recombinant hLa and hLa61-84 peptide but not recombinant mouse La. Positive selection occurred and was equivalent in 3B5.8 Tg mice of H-2k/k and H-2k/b haplotypes but was not observed in the presence of H-2b/b. Thymic deletion of CD4+CD8-(CD4SP) Vbeta10 + cells occurred in 3B5.8/hLa double Tg, H-2k/k mice but was incomplete in H-2k/b mice. Both Vbeta10+CD25 +Foxp3- and Vbeta10+CD25+Foxp3 + CD4SP thymocyte numbers were increased in 3B5.8/hLa double 16 Tg, H-2k/b mice and developed exclusively in the presence of self hLa Ag in the absence of endogenous TCRalpha. Strikingly, the relative abundance of these two populations was reversed in the periphery compared to thymus, with the Foxp3- population dominating in the thymus. Development of Vbeta10+CD25+Foxp3- and Vbeta10+CD25+Foxp3+ CD4SP thymocytes was associated with less efficient presentation of hLa by H-2k/b APC and maintenance of serologic tolerance to hLa. The thymic Vbeta10 +CD25+Foxp3- CD4SP population was identified as a viable Treg precursor as evidenced by an Annexin Vlow PI- phenotype and upregulated expression of GITR, CD44, and CD69.;These studies identify thymic deletion and CD25+Foxp3 + natural regulatory T cell (Treg) development as important mechanisms of CD4+ T cell tolerance to an RNA-binding nuclear autoantigen and demonstrate an avidity threshold that precludes Ag-specific Treg development.