SH3 dependent cell death signaling of the avian chB6 alloantigen.

In chickens, B cells develop in the bursa of Fabricius, a unique organ for B cell development. Most B cells will die within the bursa, mirroring cell losses seen in mammalian bone marrow as central tolerance is enforced at the transition to mature cells. B cell responses are shaped by a complex interplay of signals. Signals in addition to BCR that impact central tolerance have recently been described. We have been interested in chB6, a novel alloantigen on B cells in the chicken. chB6 is found in close proximity to the BCR and can trigger apoptosis after cross-linking by antibody. chB6 has two Ig domains, placing it within the CD2/SLAM family of molecules, but its cytoplasmic domain is unique. We have used a site-specific mutagenesis approach to show that an SH3 binding site in chB6 is required for the induction of apoptosis, suggesting parallels to CD2 signaling.