EVIDENCE FOR ADHESIN ACTIVITY IN THE ACID-STABLE MOIETY OF THE PHOSPHOMANNOPROTEIN CELL-WALL COMPLEX OF CANDIDA-ALBICANS

Previously, we showed that Candida albicans hydrophilic yeast cells ad here specifically to mouse splenic marginal-zone macrophages. The adhe sins are part of the yeast cell wall phosphomannoprotein complex, and one adhesin site, which reacts with the monoclonal antibody 10G, was i dentified as a beta-1,2-linked tetramannose in the acid-labile portion of the complex. We report here that the acid-stable part of tile comp lex, which has not been reported previously to have adhesin activity, is in large part responsible for yeast cell binding to the splenic mar ginal zone. The phosphomannoprotein complex, termed Fr.II, was isolate d from C. albicans serotype B yeast cells by beta-mercaptoethanol extr action and concanavalin A-agarose affinity chromatography. Fr.II is de void of the serotype A-specific antigen factor 6, which functions in y east cell attachment to epithelial cells. The acid-stable part of Fr.I I (i.e., Fr.IIS) was obtained by mild acid hydrolysis and size exclusi on fractionation. Fr.IIS was further fractionated into four fractions, Fr.IIS1, Fr.IIS2, Fr.IIS3, and Fr.IIS4, by concanavalin A-agarose col umn chromatography and elution with a linear gradient of alpha-methyl- D-mannopyranoside. Adhesin activity of these fractions was determined by their ability to block yeast cell binding to the splenic marginal z one. Fr.IIS1 and Fr.IIS2 yielded more material and stronger adhesin ac tivity than either Fr.IIS3 or Fr.IIS3. Only Fr.IIS1 did not react with antibodies (anti-factor 5 and monoclonal antibody 10G) specific for t he acid-labile beta-1,2-linked oligosaccharides. Fr.IIS1-coated latex beads attached specifically to the marginal zone in a pattern identica l to that of yeast tell binding. Furthermore, Fr.IIS1-latex bead attac hment was inhibited by soluble Fr.II or Fr.IIS. Initial chemical analy ses indicate that the adhesin site on Fr.IIS1 is a carbohydrate becaus e adhesin activity was destroyed by periodate oxidation but not by pro teinase K digestion.