CD4(+) T cells from MHC II-dependent thymocyte-thymocyte interaction provide efficient help for B cells.

Recently, a novel CD4(+) T-cell developmental pathway was reported that generates thymocyte-thymocyte (T-T) CD4(+) T cells. We established a mouse system (CIITA(tg)CIITApIV(-/-)) where thymic positive selection occurred only by major histocompatibility complex (MHC) class II+ thymocytes. T-T CD4(+) T cells selected via MHC class II-dependent T-T interaction are comprised of PLZF-negative and innate PLZF-positive populations. Until recently, the functional role of the PLZF-negative population was unclear. In this study, we demonstrate that naive T-T CD4(+) T cells provide B-cell help to a level comparable with that of naive conventional CD4(+) T cells. Considering the absence of PLZF expression in naive T-T CD4(+) T cells, these results suggest that PLZF-negative naive T-T CD4(+) T cells are functionally equivalent to conventional naive CD4(+) T cells in terms of B-cell help. Immunology and Cell Biology (2011) 89, 897-903; doi:10.1038/icb.2011.8; published online 1 March 2011