CD5(-CELL-DEPENDENT REGULATION OF THE MURINE T-CELL INDEPENDENT IMMUNE-RESPONSE AGAINST THE HUMAN BLOOD-GROUP-A ANTIGEN() B)

The CD5(+)B lymphocyte (B1a) population is known to be involved in mos t immune responses to microorganism Tl antigens. Moreover, xid mice de ficient for immune responses against Tl-2 antigens are known to lack t he B1a population, suggesting a role for B1a cells in Tl-2 immune resp onses. We previously established that the oligosaccharide human blood group A antigen stimulated murine Tl-2 immune responses. In this work, we show that the frequency of anti-A-secreting hybridomas was higher in mice with larger splenic B1a populations and that in vivo anti-CD5 treatment reduced anti-A immune response without affecting the respons e against TD RBC antigens. A similar effect was observed by in vitro a nti-CD5 treatment of splenocytes. The in vivo anti-CD5 treatment also interfered with the immunization-dependent increase in splenocyte numb ers. These results are in agreement with an important role for the B-c ell CD5 receptor in the regulation of Tl-2 immune responses possibly m ediated by its interaction with the CD72 ligand.