Alterations of the immune response associated with chronic experimental leishmaniasis.

BALB/c mice infected with Leishmania mexicana developed a chronic infection usually accompanied by the appearance of metastatic lesions. Throughout the 20 weeks of observation, infected mice ;howed an impairment in both in vivo delayed hypersensitivity response and in vitro lymphocyte reactivity to leishmanial antigen. Four to 8 weeks after inoculation infected mice displayed a transitory enhancement of spleen cell responses to phytohemagglutinin P, concanavalin A, and lipopolysaccharide. At the same time, immunization with sheep erythrocytes resulted in a greater number of immunoglobulin P, lipopolysaccharide, and sheep erythrocytes diminished progressively, whereas reactivity to concanavalin A was markedly augmented. When cocultivated with spleen cells from mice infected for 12 to 20 weeks, normal lymphocyte responses to phytohemagglutinin P, concanavalin A, and lipopolysaccharide were drastically reduced. These results suggest a role for suppressor cells in chronic experimental cutaneous leishmaniasis.