An iC3b Receptor on Candida albicans: Structure, Function, and Correlates for Pathogenicity

TLDR

Membrane receptors for complement fragments are known only in mammalian cells, where they trigger phagocytic responses to microbial invasion. The study investigates whether Candida albicans expresses surface receptors for the complement fragment iC3b. These receptors, homologous to the α‑chain of neutrophil iC3b receptors, are induced by mycelial transformation and high glucose, bind iC3b noncovalently, and impair phagocytic uptake by polymorphonuclear leukocytes. The authors found that iC3b receptors on C.

Abstract

Heretofore, the existence of membrane receptors for biologically active fragments of ammalian complement proteins has been confined to mammalian cells, where these receptors serve to protect the host by triggering multiple aspects of the phagocytic response to microbial invasion. In this study, we show that surface receptors for the C3 fragment iC3b are present on the yeast Candida albicans, where they promote the pathogenicity of this organism by inhibiting phagocytosis. These receptors share homology with the α-chain, but not with the β-chain, of neutrophil receptors for iC3b, as determined by the binding of monoclonal antibodies, and are induced by mycelial transformation of the yeast and by high concentrations of glucose. Blockade of these receptors by monoclonal antibodies significantly augments phagocytosis for those strains studied. By binding iC3b noncovalently, these receptors impair phagocytic uptake of C. albicans by human polymorphonuclear leukocytes.