Binding of plasma proteins to Candida species in vitro

The ability of purified human albumin, fibrinogen and transferrin to bind to Candida species was measured by immunofluorescence. The proteins all bound with high avidity to germ-tubes formed by Candida albicans, but did not bind to blastospores of C. albicans or other pathogenic Candida species, not even to parent blastospores bearing germ-tubes. The extent of binding of the proteins to C. albicans germ-tubes varied between growth media and from germ-tube to germ-tube. Strains of C. albicans that did not form germ-tubes were incapable of binding any of the proteins. There was evidence that purified fibrinogen bound to germ-tubes with higher avidity than albumin and transferrin. When germ-tubes were treated with whole human plasma or serum, indirect immunofluorescence revealed that proteins were bound all over the surface of C. albicans blastospore-germ-tube units, indicating behaviour different from that seen with the purified proteins tested alone or in mixtures. C. albicans cells grown in the presence of azole antifungal agents bound purified plasma proteins in the same way as cells untreated with the drugs. The results of this study suggest that binding of host proteins to the surface of C. albicans may not be a property related directly to virulence of the fungus in vivo.