FIGURE 4.

Demonstration of rapid and enhanced complement activation on additional Cap+ group W and Y strains of N. meningitidis. Group W strain LNP19995 and group Y strain Y2225 that lacked LOS sialic acid, fHbp, and NspA were incubated with C2-depleted human serum (25% (v/v)) for 10 min and iC3b deposited on bacteria was analyzed by Western blotting. Strains W171 and Y2220 that had been used in previous experiments were used as controls to facilitate comparison. Following incubation with serum, half the samples were treated with 1 m methylamine, pH 11, to disrupt ester linkages between the α₁′ chain of iC3b and its targets; amide linkages between iC3b and its targets remain unaffected with methylamine treatment. The position of the free 68-kDa α₁′ chain of iC3b is indicated. “α₁′ + L” indicates the position of the LOS-iC3b adduct (36). The asterisks indicate the anti-iC3b-reactive high molecular mass complexes that are seen only in the encapsulated strains and are decreased in intensity following methylamine treatment. Loading controls (Coomassie stain) and controls where bacteria are incubated with heat-inactivated serum (HIS) are as described in the legend to Fig. 3.