Human defenses against Cryptococcus neoformans: an update.

Cryptococcus neoformans var. neoformans is an opportunistic fungal pathogen, especially in AIDS patients, and is found world-wide. On the other hand, Cryptococcus neoformans var. gatti (CN-g) is restricted to an association with two species of Eucalyptus trees. Alveolar macrophages (AM) constitute the first line of defense to Cryptococcus neoformans and offers some resistance. The inflammatory response to Cryptococcus neoformans with an influx of neutrophils and monocytes affords a second line of defense. Secretion of proinflammatory monokines by human AM is now being defined. The inflammatory phagocytes are efficient in killing Cryptococcus neoformans and offer strong resistance. T and B cell responses to infection, a third line of defense, results in production of lymphokines (IFNg, etc.) and specific antibodies. Enhancement of lymphocyte responses by IL-12 and IL-18 to Cryptococcus neoformans infection appears to be critical. Susceptibility of AIDS patients to Cryptococcus neoformans is associated with low CD4+ T cell counts and likely reduced efficacy of the second line of defense.