Allergy and immunity to fungal infections and colonization.

Innate and cell-mediated immunity are considered as the principal defence lines against fungal infections in humans. Most opportunistic mycoses occur in individuals with defective innate and/or adaptive cellular immunity. The morbidity and mortality rates associated with infections caused by fungal pathogens are high, and prevention, diagnosis and treatment of these infections remain quite difficult. A variety of pathological conditions, including impaired immune function, are believed to cause host susceptibility to fungal infections as well as to determine the severity and characteristics of the associated pathology. Nonspecific cellular immunity, mediated by macrophages, neutrophils and natural killer cells, provides efficient protection against fungal infections in healthy individuals. A major reason for the increase in systemic mycoses is undoubtedly related to an increased number of patients with congenital or acquired immunodeficiencies. However, there is increasing clinical and experimental evidence indicating that antigen-specific cellular immunity may also play a critical role in host protection against fungi. A better understanding of reciprocal regulation between innate, humoral and adaptive immune responses in the development of an optimal antifungal immunity and, in particular, the improved definition of fungal antigens, may lead to a clarification of the mechanisms involved in host immunity to fungal infections. Molecular cloning and characterization of fungal antigens reveals the involvement of related cross-reactive molecular structures produced by different fungi as pathological molecules involved in development of allergic reactions.