Activation of the alternative complement pathway by Fonsecaea pedrosoi.

Human sera were examined for evidence of complement activation by Fonsecaea pedrosoi. The serum that had been incubated with F. pedrosoi showed immunoelectrophoretic C3 conversion and generation of C5a, as measured by radioimmunoassay. C3 conversion and C5a generation did not occur in serum chelated with EDTA, or in serum heated to 56 degrees C for 30 min. Serum depleted of the heat (50 degrees C X 30 min)-labile factor B was also deficient in C3 conversion and C5a generation. Complement activation was not affected when the classical pathway was blocked by Mg++-EGTA. These studies indicate that F. pedrosoi can activate the complement system via the alternative pathway, with the resultant development of C5a.