FIG 1.

(A and B) C4b deposition is undetectable on different strains and serotypes of encapsulated (A) and nonencapsulated (B) S. pneumoniae. Microtiter plates were coated with formalin-fixed bacteria and incubated with serial dilutions of human serum. C4 was detected using chicken anti-human C4b. In both the experiments, C4b deposition could not be detected on any of the pneumococcal strains. Mannan and E. coli were used as positive controls. The results are means ± the standard errors of the mean (SEM) of three different experiments. The differences between the controls (mannan and E. coli) and the S. pneumoniae strains were significant (P < 0.001); there were no differences among the S. pneumoniae strains (two-way analysis of variance [ANOVA] with Dunnett’s correction for multiple comparisons).