ABSTRACT
This chapter examines the immunologic regulation of certain potent macrophage effector reactions that influence the balance between host survival and parasite replication: those that prevent the parasite from entering its host cell, and those that alter the intracellular environment of the macrophage so that the parasite is unable to survive or replicate. In the hierarchy of intracellular pathogens, the Leishmania surely rank at, or near the top of the list in selectivity. In their mammalian hosts, these protozoan parasites infect only cells of the monocyte/macrophage lineage. The genus Leishmania is composed of several genetically and physiologically distinct species that are introduced into the human through the bite of a sandfly. Fundamental to establishment of intracellular infection is parasite entry into the host cell. Susceptibility or resistance to infection, then, depends on the efficiency with which infection of individual cells occurs.
