title: The microbicidal activity of interferon-gamma-treated macrophages against Trypanosoma cruzi involves an L-arginine-dependent, nitrogen oxide-mediated mechanism inhibitable by interleukin-10 and transforming growth factor-beta.
abstract: The present study was carried out to determine the effector mechanism of anti-Trypanosoma cruzi activity by interferon (IFN)-gamma plus lipopolysaccharide (LPS)-treated macrophages. A macrophage cell line (IC-21) that failed to mount an appreciable oxidative burst was nevertheless found able to control T. cruzi growth after exposure to IFN-gamma alone or IFN-gamma plus LPS. Moreover, microbicidal functions of both inflammatory macrophages and IC-21 against T. cruzi was found to be inhibited in the presence of NG-monomethyl-L-arginine (NGMMA), a competitive inhibitor of L-arginine. Addition of supplemental L-arginine to the culture overcame the capacity of NGMMA to block activated macrophage anti-T. cruzi functions. The ability of NGMMA to reverse both parasite growth inhibition and killing by IFN-gamma plus LPS-activated macrophages was found to correlate with the suppression of nitrite accumulation in the culture supernatants. Together, these results implicate the L-arginine-dependent production of nitric oxide in T. cruzi killing by activated macrophages. We also tested the ability of interleukin(IL)-10 and transforming growth factor (TGF)-beta, to block regulation of T. cruzi growth in this system. Both IL-10 and TGF-beta inhibited anti-parasite function by IFN-gamma-activated macrophages, with an optimal dose of 100 units/ml and 0.5 ng/ml, respectively. Moreover, when used in combination, suboptimal doses of IL-10 and TGF-beta were found to produce a synergistic inhibitory effect in the regulation of T. cruzi growth. The ability of IL-10 and TGF-beta to suppress microbicidal function was also positively correlated with inhibition of nitrite generation in macrophage culture supernatants. These results predict an in vivo role for IL-10 and TGF-beta in promoting parasite survival in the face of the host cell-mediated immune response.
authors.affiliation: Immunology and Cell Biology Section, NIAID, National Institutes of Health, Bethesda, MD 20892.
authors.forename: R T
authors.initials: RT
authors.lastname: Gazzinelli
authors.forename: I P
authors.initials: IP
authors.lastname: Oswald
authors.forename: S
authors.initials: S
authors.lastname: Hieny
authors.forename: S L
authors.initials: SL
authors.lastname: James
authors.forename: A
authors.initials: A
authors.lastname: Sher
mesh_terms: D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D002460:Cell Line; D005260:Female; D007371:Interferon-gamma / Q000494:pharmacology*; D016753:Interleukin-10 / Q000494:pharmacology*; D008262:Macrophage Activation / Q000187:drug effects; D008264:Macrophages / Q000187:drug effects* / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D009569:Nitric Oxide / Q000378:metabolism*; D016897:Respiratory Burst; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014349:Trypanosoma cruzi / Q000254:growth & development*; D019323:omega-N-Methylarginine
chemical_list: D016212:Transforming Growth Factor beta; D016753:Interleukin-10; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D007371:Interferon-gamma; D001120:Arginine