Effect of outer membrane protein P5 on IgM, IgG, phosphorycholine and C3 binding to the bacterial surface. NTHi R2866 and R2866ΔompP5 mutant were incubated for 15 min in media alone (Ab control) or in media containing 5% NHS or TEPC-15 that recognizes phosphorylcholine. Binding of IgG (n = 7) (A), IgM (n = 6) (B), TEPC-15 (n = 7) (C) or complement factor C3 (n = 6) (D) to the bacterial surface was determined by flow cytometry and compared by measurement of geometric mean fluorescence intensity (MFI) in arbitrary units (AU). NTHi R2866 and R2866ΔompP5 mutant were incubated for 15 min in 5% NHS, 5% C1q-depleted NHS or 5% factor B-depleted NHS and binding of C3 was determined by flow cytometry and compared by measurement of geometric mean fluorescence intensity (MFI) in arbitrary units (AU) (n = 4) (E). Statistical significance was determined with an unpaired Student’s t-test (A–D) or with a two-way ANOVA and the Bonferroni post hoc test (E). NS, not significant; *P < 0.05.