Biochemical and antigenic characterization of mannoprotein constituents released from yeast and mycelial forms of Candida albicans.

Yeast or mycelial cultures of Candida albicans released comparable amounts of Concanavalin A-reactive mannoprotein material after 24-h of growth, and in both cases this material showed a qualitatively similar SDS-PAGE pattern, with predominantly polydisperse constituents of high molecular mass. The two secretion mixtures also showed similar reactivity by ELISA with serum from a subject with high titre anti-Candida antibodies, as well as with an anti-Candida hyperimmune antiserum raised in rabbits. Both secreted extracts were separated by ion-exchange chromatography into two major fractions (designated F1 and F2), each containing mannoprotein antigens recognized by rabbit and human sera, although the immunoreactivity of the two fractions from the two growth forms was not uniform. The mannoproteins released from mycelial cultures, in particular those present in the F1 fraction, were poorly reactive or not reactive at all in ELISA with a monoclonal antibody (mAbAF1) which strongly recognized the material released from yeast cultures. Immunoblots of the more acidic, more antigenic F2 fractions with mAbAF1 and polyclonal anti-Candida antisera demonstrated that the monoclonal antibody did not recognize several mannoprotein molecules which were recognized by the polyclonal antibodies, in particular a 45-47 kDa component present only in the secreted extract from mycelium. A quantitative ELISA-inhibition method showed that the rate of release of mannoprotein antigen during growth in the yeast form was either constant (as assayed with polyclonal antibodies) or fluctuated without any definite trend (as seen with mAbAF1). On the other hand, cultures of mycelial cells exhibited an early (90 min) peak of antigen release, followed by either a decrease to a rate corresponding to that of yeast cells (with polyclonal antibodies) or a total lack of secretion (with mAbAF1). This modulation in the secretion of mAbAF1 reactive molecules was temporarily associated with germ tube emergence-elongation, and was not observed in an agerminative mutant of C. albicans grown under germination permissive conditions. These results highlight the dynamic aspects of the secretion of specific mannoprotein epitopes released from C. albicans during hyphal growth, and the direct relationship between this release and the dynamic expression of the same epitopes on the cell surface demonstrated previously.