Suppression of immunity and inflammation by products produced by dermatophytes.

When normal, previously uninfected hosts are exposed to dermatophytes under experimental occlusive conditions, infections develop and cell-mediated immunity is induced. Subsequent exposure to dermatophytes under the same conditions elicits an immune response that is capable of curing the infection, once occlusion is removed. Lymphocytes or monocytes involved in the immune response may produce cytokine growth factors that foster stratum corneum turnover and shedding of the fungus from the skin surface. Chronic dermatophyte infections develop when conditions of the local environment or virulence factors of the fungus outweigh the capabilities of cell-mediated immunity, or when a person does not develop cell-mediated immunity to fungal antigens. Even if immunity does develop, certain dermatophytes such as Trichophyton rubrum produce substances that diminish the immune response. One class of these substances, the mannans, can indirectly inhibit stratum corneum turnover. A nonresponsive host immune system or the suppression of the immune response by products produced by dermatophytes can prevent complete eradication of the fungus or predispose to reinfection.