Pneumococcal Type-Associated Variability in Alternate Complement Pathway Activation.

摘要

Opsonization of Streptococcus pneumoniae may be mediated by the alternate complement pathway. Complement consumption by pneumococci of various serotypes was measured in human serum chelated with ethyleneglycoltetraacetic acid, a substance that blocks the classic but not the alternate complement pathway. Serotype I, in contrast to all other types studied, lacked ability to consume complement in this system. The ability of serotypes III, IV, and VIII to activate the alternate pathway could be eliminated by prior serum absorption at 0 C with the type in question, a condition that would remove antibody but not complement. Types VII, XII, XXV readily activated the alternate pathway in unabsorbed and absorbed sera. It was concluded that types I, III, IV, and VIII lack intrinsic ability to activate and thus be opsonized by the alternate complement pathway, although types III, IV, and VIII can do so in concert with specific antibody. The fact that these same types are especially prominent in human disease suggests that the ability to evade opsonization by the alternate complement pathway in pre-antibody phases of infection may be a virulence factor in pneumococci.