MODULATION OF CD72 BY LIGATION OF B-CELL RECEPTOR COMPLEX-MOLECULES ON CD5(-CELLS() B)

B cells expressing CD5 also carry its ligand, CD72, As an approach to understanding the role of CD5 and CD72 on B cells, we have examined th e association of CD72 with CD5 and slgM by modulation/co-modulation an d capping/co-capping following ligation of these surface molecules wit h specific antibodies, Modulation and co-modulation were measured afte r 24 h, whilst capping was measured after 1 h, CD5 and slgM co-modulat ed each other, CD72 co-modulated with slgM and CD5, but anti-CD72 did not affect either slgM or CD5, CD5 and slgM co-capped each other, whil st CD72 failed to co-cap with either slgM or CD5, The CD5-induced co-m odulation of CD72 was partially blocked by specific protein tyrosine k inase inhibitor, but not the slgM-induced co-modulation. Protein kinas e C (PKC) inhibitors abrogated the anti-mu- but not the anti-CD5-trigg ered modulation of CD72, whereas PKC activators prevented the CD5- but not the slgM-induced 24 h modulation of CD72, None of these drugs was able to modify the anti-CD72-induced modulation of CD72, Our data sug gest that CD5 is physically associated with slgM in the B cell recepto r complex but not with CD72, Furthermore, from the effect of drugs on modulation, there appears to be different associations of CD72 with sl gM and CD5, These two pathways differed in some respects, consistent w ith a co-stimulatory function of CD72 and CD5 in B cell activation.