Influence of CR2 and CR1 blockade on C3-fragment deposition and MAC formation on B cells. The percentage of C3d-specific (open columns) and C9-specific (solid columns) fluorescence, respectively, relative to incubation in normal human serum (NHS)/Mg/EGTA, in the absence of blocking antibodies, is given. B cells were incubated under the given conditions in the presence of the CR2-blocking mAb FE8, the CR1-blocking mAb 3D9 or the control mAbs HB135, for CR2 and HB8592, for CR1. The error bars display the 95% confidence intervals for the values obtained with sera from six donors.