Complement activation by pneumococci associated with acute otitis media.

Pneumococci (types, I, III, VI, XIV, XVIII, XIX and XXIII) associated with acute otitis media were shown to activate complement in normal human serum by the classical as well as by the alternative pathway. In serum incubated with pneumococci classical pathway activation was demonstrated by decreased C4 values and the appearance of C1r-C1s-C1 IA complexes. Pneumococci caused C3 conversion in C2-deficient serum and in serum chelated with Mg++ EGTA showing activation of the alternative pathway without participation of the C42 convertase. Complement activation was more efficient when both pathways were intact. This was evident from a more pronounced C3 conversion and a greater reduction of the values for properdin and factor B in non-chelated serum as compared to Mg++ EGTA chelated serum.