Reactivity of Candida albicans Germ Tubes with Salivary Secretory IgA

Abstract

Salivary secretory IgA (sIgA) has been shown to react with a group of heat shock mannoproteins preferentially expressed on yeast cells grown at 37°C. Since at this temperature C. albicans can induce germ tubes, we explored the role of germ tube induction on human salivary sIgA reactivity in both germinative and agerminative C. albicans strains, in an attempt to investigate whether the germ tube expressed the heat shock mannoproteins reactive with sIgA. The reactivity with sIgA of the agerminative strain, grown at 25 and 37°C for different times, was measured spectrofluorometrically and was fairly constant with time. Yeast cells grown at 37°C tended to be more reactive than those grown at 25°C. In contrast, when compared with the yeast cells of the germinative strain grown at 25°C, there was a statistically significant decrease in reactivity with sIgA during germ tube formation. Serum IgA and IgG did not show statistically significant changes in reactivity with C. albicans during germination, suggesting differences in reactivity with C. albicans cell wall antigens between mucosal and systemic humoral responses. Cell wall mannoproteins of molecular masses > 60 kDa were characterized by Western blotting as responsible for the decrease in sIgA reactivity observed in the germ tube, and the fall in sIgA reactivity was related to the release of cell wall mannoproteins into the culture medium. The release of these mannoproteins may be a mechanism whereby C. albicans avoids the action of sIgA, and it may play an important role in the host-parasite relationship in oral candidiasis.