Immunology of fungal infections in animals

The nature of immunity to fungal infection is discussed predominantly for mammals and birds. T-cell-mediated immunity seems essential for recovery both from cutaneous and mucosal infections (Candida, Malassezia and dermatophytes) and from infections of systemic fungal pathogens (Cryptococcus, Blastomyces, Histoplasma, and Coccidioides). Often chronic progressive disease caused by these fungi is associated with a depression or absence of T-cell-mediated immunity to antigens of the infecting fungus. In contrast recovery from disease, or absence of clinical disease after exposure to these fungi, is associated with the presence of strong T-cell-mediated immune responses to the fungus. The activation of macrophages and the stimulation of epidermal growth and keratinization are the processes induced by T-cell-mediated immunity which result in the resolution of systemic or cutaneous and mucosal disease. Other cell types, for example NK cells and PMNs (polymorphonuclear leucocytes), may be important in these diseases in reducing the effective amount of inoculum to which an animal is exposed and thereby reducing the likelihood of disseminated disease. Invasive opportunistic fungi (Candida, Aspergillus, Mucorales) are resisted by PMNs which attach to the hyphae or pseudohyphae and damage them via an extracellular mechanism. Other host cell types may be important in natural resistance, fungal spores being handled by the macrophages which, under conditions when animals are not immunosuppressed, are likely to be an effective first line of defense. Subcutaneous pathogens and miscellaneous other fungal diseases are discussed from a point of view of host immunity and immunodiagnosis. Vaccine development for ringworm and for other mycoses is discussed.