The B-cell-specific src-family kinase Blk is dispensable for B-cell development and activation

The B-cell lymphocyte kinase (Blk) is a src-family protein tyrosine kinase specifically expressed in B-lineage cells of mice. The early onset of Blk e xpression during B-cell development in the bone marrow and the high express ion levels of Blk in mature B cells suggest a possible important role of Bl k in B-cell physiology. To study the in vivo function of Blk, mice homozygo us for the targeted disruption of the blk gene were generated, In homozygou s mutant mice, neither blk mRNA nor Blk protein is expressed. Despite the a bsence of Blk, the development, in vitro activation, and humoral immune res ponses of B cells to T-cell-dependent and -independent antigens are unalter ed, These data are consistent with functional redundancy of Blk in B-cell d evelopment and immune responses.