The role of complement and antibody in opsonization and intracellular killing of Candida albicans.

The purpose of this investigation was two-fold. The first, to explore the relationship between ingestion (measured by the phagocytic index method), iodination (measured by the neutrophil iodination micromethod) and intracellular killing (measured by the methylene blue test) of Candida albicans by human polymorphonuclear leucocytes. The second, to determine the effects of complement and antibody on ingestion and intracellular killing of C. albicans. Optimal phagocytosis of C. albicans was observed in fresh untreated human serum. Phagocytosis was present but reduced, in serum depleted of either antibody (by absorption) or complement (by heating at 56 degrees C for 30 min). Whilst in the complete absence of serum, or in FCS the levels were reduced still further. The percentage killed of ingested C. albicans remained constant irrespective of the number of organisms ingested, thus the greater the number ingested, the greater the number killed. Maximal intracellular killing expressed as a percentage of ingested Candida occurred in fresh untreated serum. Intracellular killing did occur in heat-inactivated serum and absorbed serum, although the levels were significantly reduced. The results suggest that C. albicans opsonized in fresh normal PHS are phagocytosed as well as killed more efficiently than those opsonized with only complement or antibody.