FIG. 6.

C3 deposition on streptococci. Bacterial cells were suspended in VBS containing 10 mM EGTA and 5 mM MgCl₂. The suspensions were mixed with an equal volume of human serum or heat-inactivated human serum (HIS) and incubated at room temperature for 30 min. Bacteria were harvested, washed, and suspended in carbonate buffer. The cells were then diluted in carbonate buffer to final OD₅₆₀s of 0.025 (open bars), 0.05 (hatched bars), and 0.1 (filled bars) and applied to wells of microtiter plates. C3 deposition was detected with a monoclonal anti-human C3d antibody.