Complement levels in Brazilian children during and after meningococcal meningitis.

PURPOSE To evaluate the functional activity of the classical and alternative pathways of the complement system and the levels of C3, C4, and factor B during the first episode of meningococcal infection and during the convalescence period. PATIENTS AND METHODS Ten Brazilian children ranging in age from 8 months to 8 years, admitted from 1991 to 1993 with a clinical-laboratory diagnosis of meningococcal meningitis, were studied during acute infection (up to 7 days from diagnosis) and during the convalescence period (1 to 6 months after the acute episode). C3, C4, and Factor B were measured using nephelometry, and the lytic activity of classical and alternative pathways were evaluated by a kinetic method and expressed as the time needed to lyse 50% of an erythrocyte suspension (T1/2, expressed in seconds). Low T1/2 values for classical and alternative pathways correlate with high activities of the classical and alternative complement pathways, respectively. RESULTS A significant difference was observed between the alternative pathway lytic activity during infection and the convalescence period (282 vs 238 seconds, respectively, P = .01). No differences were detected in the other complement parameters analyzed. CONCLUSIONS In the presence of meningococcal meningitis, the alternative pathway is preferentially activated. This is probably due to the greater ability of the meningococcal endotoxin to activate this pathway in vivo.