Macrophage-parasite interactions in Leishmania infections.

Macrophages have different roles in Leishmania infections. They function as host-cells to the parasite, they present parasite antigens to the immune system, and they also act as effector cells responsible for parasite killing in the healing stages of the infection. Protein and carbohydrate ligands on the parasite surface, which interact with receptors on the macrophage membrane during phagocytosis, have been identified. Survival of Leishmania in its host cell requires a metabolic adaptation to the intracellular environment. The nutritional requirements of the microorganism must be satisfied and the deleterious effect of oxygen metabolites and of lysosomal hydrolases must be adequately counteracted. When a successful immune response develops, macrophages become activated and acquire the capacity to destroy the microorganism. Possible reasons why these mechanisms fail in certain individuals or experimental host-parasite combinations are discussed.