COMPLEMENT BINDING TO ASPERGILLUS CONIDIA CORRELATES WITH PATHOGENICITY

Complement has significant effects on the phagocytosis of Aspergillus organisms. We examined the amount and type of complement component C3 bound to the resting conidia of 29 isolates from nine Aspergillus spec ies. The highly pathogenic species A. fumigatus and A flavus bound few er C3 molecules per unit of conidial surface area than did the less pa thogenic species A glaucus, A nidulans, A niger, A ochroceus, A terreu s, A versicolor, and A wentii, as determined by quantitative flow cyto metry. immunoblot analysis of C3 fragments bound to conidia demonstrat ed that for all species most C3b was apparently converted to iC3b. For seven species, iC3b was clearly the major C3 product recognized by im munoblotting. However, A niger and A nidulans appear to promote furthe r breakdown of opsonic C3 fragments to C3dg. We found significant vari ations in size and C3 binding among isolates within the same species. Intraspecies variation may contribute to seemingly discrepant results obtained in studies of Aspergillus phagocytosis.