Unexpected Role for the B cell-specific Src Family Kinase Blk in the Development of IL-17-Producing gamma/delta T Cells

The Ag receptors on alpha/beta and gamma/delta T cells differ not only in the nature of the ligands that they recognize but also in their signaling potential. We hypothesized that the differences in alpha/beta - and gamma/delta TCR signal transduction were due to differences in the intracellular signaling pathways coupled to these two TCRs. To investigate this, we employed transcriptional profiling to identify genes encoding signaling molecules that are differentially expressed in mature alpha/beta and gamma/delta T cell populations. Unexpectedly, we found that B lymphoid kinase (Blk), a Src family kinase expressed primarily in B cells, is expressed in gamma/delta T cells but not in alpha/beta T cells. Analysis of Blk-deficient mice revealed that Blk is required for the development of IL-17-producing gamma/delta T cells. Furthermore, Blk is expressed in lymphoid precursors and, in this capacity, plays a role in regulating thymus cellularity during ontogeny. Naive alpha/beta and gamma/delta T cells isolated from mouse lymph nodes and purified by negative selection were compared using MOE430 2.0 GeneChip.