title: IL-10 inhibits parasite killing and nitrogen oxide production by IFN-gamma-activated macrophages.
abstract: IL-10, a cytokine produced by CD4+ T lymphocytes belonging to the Th-2 subset, has previously been shown to inhibit the synthesis of IFN-gamma by both T cells and NK cells. We now demonstrate that IL-10 can also down-regulate IFN-gamma-dependent immunity by blocking the ability of that lymphokine to activate macrophages. Thus, IL-10, in a dose-dependent manner, inhibits the microbicidal activity of IFN-gamma-treated inflammatory macrophages against intracellular Toxoplasma gondii as well as the extracellular killing of schistosomula of Schistosoma mansoni. This suppression correlates with the inhibition by IL-10 of IFN-gamma-induced production of toxic nitrogen oxide metabolites, an effector mechanism previously implicated in the killing by macrophages of both parasite targets. IL-10 inhibition of nitric oxide production was shown to occur when the cytokine is given before or together with the IFN-gamma-activating stimulus, but not after its removal from the cultures and to require 12 h of contact for maximal suppressive effect on macrophage function. These results, taken together with previous findings on the down-regulation of Th1 lymphokine production by IL-10, indicate that the induction of IL-10 may be an important strategy by which parasites evade IFN-gamma-dependent, cell-mediated immune destruction.
authors.affiliation: Immunology and Cell Biology Section, National Institute of Allergy and Infectious Disease, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: R T
authors.initials: RT
authors.lastname: Gazzinelli
authors.forename: I P
authors.initials: IP
authors.lastname: Oswald
authors.forename: S L
authors.initials: SL
authors.lastname: James
authors.forename: A
authors.initials: A
authors.lastname: Sher
mesh_terms: D000818:Animals; D003602:Cytotoxicity, Immunologic / Q000187:drug effects; D007111:Immunity, Cellular / Q000187:drug effects; D066298:In Vitro Techniques; D007371:Interferon-gamma / Q000494:pharmacology; D016753:Interleukin-10 / Q000494:pharmacology*; D008262:Macrophage Activation / Q000187:drug effects; D008264:Macrophages / Q000187:drug effects / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009589:Nitrogen Oxides / Q000378:metabolism*; D012550:Schistosoma mansoni / Q000276:immunology; D012555:Schistosomiasis mansoni / Q000276:immunology*; D014122:Toxoplasma / Q000276:immunology; D014124:Toxoplasmosis, Animal / Q000276:immunology*
chemical_list: D009589:Nitrogen Oxides; D016753:Interleukin-10; D007371:Interferon-gamma