Cutting edge: lack of peripheral B cells and severe agammaglobulinemia in mice simultaneously lacking Bruton's tyrosine kinase and the B cell-specific transcriptional coactivator OBF-1.

OBF-1 is a B cell-restricted transcriptional coactivator that is recruited to octamer-containing promoters by interacting with the POU domain of Oct-1 or Oct-2. We have shown earlier that mice lacking OBF-1 were dramatically impaired in their ability to mount humoral immune responses and did not develop germinal centers in the spleen; however, they had a largely normal B cell development in the bone marrow. In this study, we demonstrate that OBF-1-deficient mice also have an early defect in B cell development and show that OBF-1-/- immature B cells are greatly impaired at the transition from the bone marrow to the spleen. In addition, when the OBF-1 mutation is combined to a mutation in the gene encoding Bruton's tyrosine kinase, a striking phenotype is observed. These double-deficient animals lack peripheral B cells and have virtually no serum Igs, thus closely resembling human X chromosome-linked agammaglobulinemia.