The transcriptional regulator Rel is essential for antigen receptor-mediated stimulation of mature T cells but dispensable for positive and negative selection of thymocytes and T cell apoptosis.

The family of Rel/NF-kappaB transcription factors is a crucial regulator of various cellular responses. Using Rel-deficient (c-rel-/-) mice crossed with T cell receptor (TCR)-transgenic mice we show that Rel is neither required for positive selection of major histocompatibility complex (MHC)-restricted T cells nor for deletion of thymocytes bearing autoreactive antigen receptors. Our studies also demonstrate that Rel is dispensable for T lymphocyte apoptosis. Rel is, however, essential for antigen-induced activation of mature T cells and its absence exacerbates the anergic state. These results indicate that thymocytes and mature T cells differ in their requirement for Rel in mediating TCR-induced responses.