Dose-dependent effects of dimeric and monomeric fractions of anti-B4–bR on calcium mobilization. Dimers and monomers of IT were purified by gel filtration and tested for calcium mobilization in Namalwa cells. Data are expressed as the peak values of percent increase in fluorescence over basal level in cells treated with increasing concentrations of dimeric IT (□), monomeric IT (▪), or unconjugated anti-B4 (○).