CD5-positive B cells at the crossroads of B cell malignancy and nonorgan-specific autoimmunity.

The CD5 glycoprotein is detectable on a minute fraction of circulating B cells. The number of CD5+ B cells (B1 cells) is increased in patients with autoimmune disorders and these cells, similar to those leading to chronic lymphocytic leukemia (CLL), may be induced to produce multispecific autoantibodies. CD5 is associated with the B cell antigen receptor, and the induction of apoptosis depends on the activation state of the cells. Defective regulation of this phenomenon might result in the production of autoantibodies and/or the development of CD5+ B cell tumors. We have proposed that there may be different B1 populations in man, which depend on the consequence of CD5 ligation on their surface: 'natural' or 'classical' CD5+ B cells, and 'induced' CD5+ B cells.