OcaB regulates transitional B cell selection.

OcaB, also known as Bob-1 or Obf-1, is a transcriptional co-activator which regulates Igkappa gene transcription, recombination and receptor editing; it is required for normal development of transitional B cells and for germinal center formation. Here we report that abnormal B cell development in OcaB(-/-) mice results in a skewed Igkappa repertoire including anti-DNA antibodies, suggesting that OcaB is essential for antibody repertoire selection. To determine whether OcaB is required for BCR-mediated B cell selection, we introduced a pre-recombined alpha hen egg lysozyme (HEL) Ig transgene into OcaB(-/-) mice. We find that in OcaB(-/-) mice expressing transgenic alphaHEL Ig bone marrow B cell development is normal up to the immature B cell stage, but fails to progress to the transitional B cell stage. We conclude that OcaB is required for normal selection of the antibody repertoire in developing B cells.