Topical application of a corticosteroid destabilizes the host-parasite relationship in an experimental model of the oral carrier state of Candida albicans.

Using an experimental model in the mouse we have shown that both local and central lines of defense, involving CD4+ T cells, participate in a dynamic interaction to maintain a long-term carrier state of Candida albicans in the oral cavity. We have tested the impact of a predisposing factor to oral candidiasis in the form of a topical application of a corticosteroid (Topsyn gel) to the oral mucosa for 75 mice twice a day for a 20-day period. Very rapidly after the treatment was initiated, i.e. on day 4, the residual population of Candida increased up to 40-fold and by day 21, the population was 400-fold that of the carrier state. The resident population of intraepithelial CD4+ T cells in the oral mucosa virtually disappeared during the treatment. A topical corticosteroid application also resulted in a massive depletion of T cells in the lymph nodes and in the transient abrogation of the DTH reaction to Candida antigens. On cessation of treatment, normal levels of both Candida and intraepithelial CD4+ T cells were also quickly restored. These results suggest that resistance to superficial invasion by Candida is linked to the presence of an oral mucosal line of defense and that topical application of corticosteroids may dramatically shift the host-parasite relationship in favor of Candida.