Some immunochemical observations on the cell walls of yeasts

Purification of a mannan from Candida albicans which activates serum complement

Candida species activate complement by the alternative pathway, induce leukocyte migration and, when applied epicutaneously, cause epidermal microabscesses of neutrophils in man and experimental animals. Complement activation by C. albicans appears to be a property of the cell wall. To biochemically identify the complement-activating constituent(s) of C. albicans, an ethyleneglycol extract of growth phase blastospores was prepared. Acid hydrolysis and neutral sugar analysis revealed mannose (82%), fucose (7%), and glucose (11%). The soluble, mannose-rich cell wall polysaccharide of C. albicans activates serum complement via the alternative pathway, induces neutrophil chemotaxis and is antigenically reactive with antisera to C. albicans. This constituent exhibits in vitro endotoxin-like activity as measured by Limulus lysate gelation, but is nonpyrogenic in rabbits. The extracts produced precipitin lines in double immunodiffusion studies against serum from patients with invasive candidiasis and rabbit antisera to mycelial and blastospore preparations of C. albicans, but not against normal serum. Thus, pathogenic properties and reactive phenomenon of C. albicans are in part attributable to a cell wall polysaccharide, mannan.

Antigenic analysis of yeast cell-walls

Agglutination and complement fixation tests with yeast cell-walls revealed an extensive and complex pattern of cross-reactions amongst 26 species of 20 genera of yeasts. Common antigens were found in all yeast cell-walls. Ascosporogenous yeasts possessed antigens not found in the asporogenous yeasts and vice versa. Nuberical analyses of serological properties confirmed this distinction and also that little differentiation could be achieved at generic level with respect to Saccharomyces and Candida spp.

Response and specificity of antibodies for Candida albicans

Rabbit antibodies for Candida albicans, reacting in agglutination and fluorescent-antibody reactions, were present in both IgM and IgG protein fractions. The two types of immune globulins were separated from ammonium sulfate-precipitated gamma-globulin either by filtration through a column of Sephadex G-200 or by diethylaminoethyl column chromatography performed by stepwise elution with various concentrations of sodium chloride. In the fluorescent-antibody test, initial separation of the IgG fraction, prior to its conjugation with dye, proved to be essential for the high specificity of this reaction. Investigation of the specificities of the two types of antibodies revealed that the IgG was highly specific, whereas the IgM was not very specific. Each antigen fraction, extracted by various methods, demonstrated its own characteristic antibody response. Only the IgG fraction yielded serotype-specific antibody useful for detection of a serotype of C. albicans in agglutination and fluorescent-antibody tests. The results indicate the importance of IgG for specific serological reactions with the Candida species.