B-cell responses to B-cell activation factor of the TNF family (BAFF) are impaired in the absence of PI3K delta.

B-cell activating factor of the TNF family (BAFF) is critical for the survival and maturation of B cells. The molecular mechanisms by which BAFF regulates the survival of developing B cells are becoming better understood. Recent evidence has begun to emerge demonstrating a role for the PI3K/Akt signalling pathway in response to BAFF. However, the importance of the PI3K family for BAFF-signalling and the effects of loss of PI3K function on BAFF responses are still unknown. We therefore investigated the BAFF-mediated responses of B cells deficient for the PI3K catalytic subunit P110delta. We find that the loss of P110delta impairs the BAFF-mediated survival of cultured B cells demonstrating a direct role for this member of the PI3K family in regulating the survival of B cells in response to BAFF. P110delta was required for the growth of B cells in response to BAFF and was critical for the upregulation of the receptor for BAFF following BCR crosslinking. Our findings reveal an important role for p110delta in regulating B-cell responses to BAFF.