FIGURE 1.

Deletion of fHbp and NspA abrogates factor H binding to meningococcal mutants used in this study. Meningococcal strains A2594 (group A), H44/76 (group B), C2120 (group C), W171 (group W-135), and Y2220 (group Y) that lacked LOS sialic acid, but expressed capsule (Cap+/fHbp+/NspA+; solid black bars) and their isogenic mutants that were deficient in capsule production (Cap−/fHbp+/NspA+; solid gray bars) were further mutated to delete both known meningococcal factor H-binding proteins, fHbp (30, 41) and NspA (29). The Cap+ and Cap− strains that lacked fHbp and NspA are shown by the black and gray hatched bars, respectively. The five sets of isogenic mutant strains were incubated with factor H (20 μg/ml) and bacteria-bound factor H was detected using sheep polyclonal anti-human factor H followed by anti-sheep IgG-FITC. The y axis represents the median fluorescence intensity of the entire bacterial population. A representative control (factor H omitted from the reaction mixture) with group A strain 2594 is shown; all strains yielded similar control fluorescence values.