Complement in pneumococcal infections with varying degrees of severity.

Complement component levels (Clq, Cls, C4, C3, factor B and properdin) and C1 subcomponent complexes (C1r-C1s, C1-r-C1-, C1-r-C1-s-C1 inactivator, 1A) were studied in 16 adults with pneumococcal infections varying severity. Patients with fulminant disease and signs of septic shock showed pronounced hypocomplementemia. In patients with pneumococcal pneumonia or meningitis elevated levels of C1-r-C1-s-C1- IA complexes indicated activation of C1, despite normal levels of C1q, C1s, C4 and C3. Moderately decreased properdin values suggested involvement of the alternative pathway. In adults with pneumococcal otitis no changes in the complement profile was found. In contrast, pronounced aberrations of the C1 subcomponents were earlier demonstrated in children with otitis.