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RESISTANCE FACTORS IN DERMATOPHYTE INFECTIONS *

INTRODUCTION Resistance to infection depends upon many factors. Some of these are specific and involve the immune and inflammatory systems. Others are nonspecific and depend upon the virulence of the organism, the nature of the stratum corneum, the anatomical site of infection, the species of the fungus, the availability of nutrients including minerals, and nonspecific serum inhibitory factors. I wish to review these resistance factors and discuss some recent experiments from our laboratories which define interactions of fungi with complement and polymorphonuclear leucocytes as potential nonspecific resistance factors and mediators of inflammation. Dermatophytic fungi include 37 common fungi in the genera microsporum, trichophyton, epidermophyton, pityrosporon, and candida. Of these, infections with microsporum, trichophyton, and epidermophyton are generally limited to the stratum corneum, hair, and nails, whereas infections with Candida albicans (but not some other members of the candida species) infect skin and nails but also can cause sepsis and infections of internal organs. Occasionally, dermatophytic fungi have disseminated into muscle, bone, the CNS and subcutaneous tissue, but this is a very rare event, and host-fungus relationships in such patients governing susceptibility have not been defined. Dermatophytic fungi are not limited to the skin just because they require keratin. They grow vigorously on other media, and can grow on other tissue including dermis in vitro.' Some factors must limit dermatophytic infections to the stratum corneum of the epidermis. Among these factors are specific and nonspecific mechanisms of host defence. The major specific mechanism of host defence is cell-mediated immunity. Acute infections in humans are associated with inflammation, delayed hypersensitivity reactions to fungal antigens, and spontaneous cure or a favourable response to treatment. Chronic infections are associated with little inflammation, absent delayed hypersensitivity, and treatment resistance. * The antigens of dermatophytic fungi are mostly keratinases, polysaccharides (especially mannopeptides), peptides, and ribonucleic acids.zDermatophytes share many common determinants because antibodies to antigens cross react widely with antigens of fungi from other species and genera. Infection of the skin begins with colonisation. Jones, Reinhardt, and Rinaldi4 were able to induce infections readily on both immune and nonimmune volunteers by placing microaleurospores on forearm skin, and covering the skin with dampened gauze under occlusion for 96 hours. Apparently resistance to infection is only relative; if the conditions are right, infection can occur. The behaviour of experimentally-induced infection varies depending on the Presence or absence of cell-mediated immunity, as assessed