Immune response and host resistance of humans to dermatophyte infection

Clearing of dermatophyte infection depends on a cell-mediated immune response. Antibodies to fungi, although present in infected persons, are ineffective at ridding the skin of fungi. Experiments in which human volunteers were deliberately infected with dermatophytes identified two major groups on the basis of cellular immune responsiveness: (1) those who mount decisive delayed-type hypersensitivity that results in clearing of the infection, and (2) those who have absent or defective cellular immunity that prevents them from mounting an effective response to dermatophytes and thus predisposes them to chronic or recurrent dermatophyte infection. The courses of experimental infection in these two groups were compared with skin test results. The presence of an acute inflammatory infection was correlated with delayed-type (T-cell-mediated) hypersensitivity to a trichophytin skin test and the ability of persons affected in this manner to achieve mycologic cure. In contrast, chronic infection was associated with high immediate (anti- Trichophyton -IgE-mediated) hypersensitivity and low or waning delayed-type (T-cell-mediated) hypersensitivity to trichophytin. Despite this immune deficiency, these persons had a normal response to other infectious agents and skin test antigens. This type of selective and perhaps induced immune deficit may be relatively common, because persons chronically infected with a dermatophyte constitute 10% to 20% of the general population.