Activation of B lymphocytes with human serum-treated zymosan

C3 fragments fixed on zymosan particles were presented to resting human B lymphocytes. The opsonized zymosan (Ops-Z) particles induced release of leukocyte migration inhibitory factor, a slight decrease in mIgD, and a slight increase in the activation marker Blast-2. The B cells did not proceed further along the pathway of activation: they did not respond to B cell growth factor (BCGF) and Ops-Z did not synergize with other activators for BCGF response either. Thus, we found that interaction between C3 fragments and CR2 initiates the activation of human B lymphocytes, but this is limited to the early phase.