Autoreactive isotype-specific T cells determine B cell frequency.

Suppressive activities involving T-B and T-T cell interactions are important to maintain immune system homeostasis. Negative control of IgG2ab+ B cells by anti-IgG2ab T cells derived from Igha mice has been well documented. Nevertheless the real contribution of anti-IgG2ab T cells, endogenously matured in Ighb mice, in controlling IgG2ab+ B cell function has never been investigated. We previously generated anti-IgG2ab TCR-transgenic mice and showed that transgenic T cells were not deleted in the thymus and that they were responsible for a complete and chronic IgG2ab suppression. Here we show that T cells expressing high density of anti-IgG2ab TCR were positively selected in the thymus with a higher efficiency in animals expressing IgG2ab, reached peripheral lymphoid organs and negatively controlled IgG2ab serum levels. Moreover, anti-IgG2ab T cells transgenic for the single TCR chain, thus undergoing normal rearrangements and normal processes of selection, also reached the periphery and suppressed IgG2ab. Interestingly, concentration of IgG2ab in serum inversely correlated with the peripheral frequency of Ig-specific T cells. Finally, T cells able to suppress IgG2ab were obtained from Ighb non-transgenic mice, indicating that anti-2ab T cells are naturally present in the periphery of Ighb animals. We propose that IgG2ab-specific T cells contribute to determine IgG2ab serum levels in Ighb mice.