title: Macrophage activation to kill Leishmania tropica: characterization of a T cell-derived factor that suppresses lymphokine-induced intracellular destruction of amastigotes.
abstract: Factors obtained from phorbol myristate acetate (PMA)-stimulated EL-4 thymoma cells, a continuous T cell line, suppressed lymphokine-induced macrophage activation to kill intracellular Leishmania tropica amastigotes. Suppression of this macrophage effector activity was dependent upon concentration of EL-4 fluids admixed with lymphokines in infected macrophage cultures, and was not due to residual PMA or factors released from unstimulated EL-4 cells. Fluids from PMA-stimulated EL-4 cells did not affect the expression of microbicidal activity by macrophages activated in vivo as a consequence of infections with Mycobacterium bovis strain BCG, nor did they abrogate intracellular killing activities by C3H/HeJ macrophages primed by BCG infection and triggered by lymphokines in vitro. That the action of this EL-4 suppressor activity was at the priming stage of macrophage activation was confirmed by kinetic studies: EL-4 fluids added to lymphokine-treated cells in the first 4 hr of treatment completely suppressed intracellular killing of L. tropica; fluids added after 4 hr were not effective. The effects of these EL-4 factors appeared to be selective: of three effector activities of activated macrophages tested, induction of resistance to infection, tumor cytotoxicity, and intracellular destruction of L. tropica, only intracellular killing by lymphokine-treated macrophages was significantly suppressed. These T cell-derived soluble suppressor factor(s) may provide insight into mechanisms of immunosuppression during leishmanial disease and perhaps other intracellular parasitic infections.
mesh_terms: D000818:Animals; D003602:Cytotoxicity, Immunologic; D000939:Epitopes; D007108:Immune Tolerance; D007891:Leishmania / Q000254:growth & development / Q000276:immunology*; D008222:Lymphokines / Q000096:biosynthesis / Q000502:physiology*; D008262:Macrophage Activation; D008264:Macrophages / Q000276:immunology* / Q000469:parasitology; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D013491:Suppressor Factors, Immunologic; D013945:Thymoma / Q000276:immunology / Q000378:metabolism
chemical_list: D000939:Epitopes; D008222:Lymphokines; D013491:Suppressor Factors, Immunologic