Chemical definition of an epitope/adhesin molecule on Candida albicans

An antigen (Ag), as defined by reactivity with a monoclonal antibody (mAb 10G), was found on the cell wall surface and on the plasma membrane of Candida albicans yeast cells (Li, R. K., and Cutler, J. E. (1991) J. Gen. Microbiol. 137, 455-464). The 10G Ag from the cell surface location was solubilized by treatment with beta-mercaptoethanol and Zymolyase. Antigenic activity of the extract was lost following periodate oxidation, but was stable to proteolytic enzyme and heat treatments. Mannoproteins in the extract were fractionated by hexadecyltrimethylammonium bromide. A fraction containing the 10G Ag was degraded by mild acid hydrolysis and a tetrahexose eluted from a P-2 size exclusion column was found to be the epitope (10G epitope) part of the 10G Ag. By use of gas-liquid chromatography, mass spectroscopy, and H-1 proton NMR analysis, the 10G epitope was determined to be a linear beta-1,2-linked tetramannose. The 10G Ag, which was immunopurified from the Zymolyase extract, and the 10G epitope were involved in the attachment of C. albicans to mouse spleen marginal zone macrophages. Both the 10G Ag and the purified 10G epitope specifically inhibited C. albicans adherence in an ex vivo binding assay. Latex beads adsorbed with the 10G Ag or the 10G epitope adhered specifically to the splenic marginal zone macrophages. These data show that a beta-1,2-linked mannotetraose part of a C. albicans cell wall mannoprotein is an adhesin site that may play a role in pathogenesis of disseminated candidiasis.