C5 can contribute to the neutralization of SV5 and MuV. A) Total hemolytic complement activity of NHS, C5-depleted serum, and C5-depleted serum reconstituted with C5 was determined as described in Materials and methods. B) and C) One hundred PFU of SV5 (panel B) or MuV (panel C) were incubated with PBS, 1:25 dilution of NHS, with the indicated dilutions of C5-depleted serum, or C5-depleted serum reconstituted with C5. Remaining infectious titers were determined by plaque assays. Results are the average of six experiments, with error bars representing standard deviations. Number sign denotes p < 0.001 comparing C5-depleted samples to C5 reconstituted samples.