Comparison of immunosuppressive effects of cyclosporine A in a murine model of systemic candidiasis and of localized thrushlike lesions.

Candida albicans is an opportunistic human pathogen preferentially causing invasive and disseminated infection in patients with defective phagocytic defenses and serious mucocutaneous infection in patients with deficient T-cell function. Phagocytes appear to protect the host from fungal invasion even in the absence of adaptive immune mechanisms, while as-yet-undefined T-cell-dependent factors seem necessary for control of C. albicans on body surfaces. To study host defense mechanisms on body surfaces, we developed a new model of thrush in artificial pneumatized cysts in mice. Cyclosporine A, a relative selective suppressor of T-cell-mediated immunity and natural killer cell activity, promoted the formation of thrushlike lesions on cyst surfaces and impeded elimination of C. albicans from such lesions. As expected from the absence of an impairment of antimicrobial phagocytic activity, cyclosporine A had no effect on systemic candidiasis induced by intravenous inoculation. Surprisingly, athymic nude mice were not more susceptible to superficial candidiasis than control mice and were comparably affected by cyclosporine A. In contrast, beige mice, which in addition to phagocytic dysfunction have reduced natural killer cell activity, were more susceptible to thrushlike lesions, and cyclosporine A was correspondingly less active in this mouse strain. Immunosuppression with cyclosporine A affects host defense mechanisms which are operative against superficial candidiasis but appear superfluous in resistance to the invasive form of this mycosis, an indication for the divergent nature of host defense against the two forms of candidiasis.