title: Interleukin-2 suppresses activated macrophage intracellular killing activity by inducing macrophages to secrete TGF-beta.
abstract: Phorbol myristate acetate (PMA) treatment of an EL-4 thymoma cell line (EL-4FARRAR) induced secretion of a factor that inhibited intracellular killing of Leishmania major amastigotes by activated macrophages. Analysis of the cytokines produced by EL-4 cells after PMA stimulation identified interleukin-2 (IL-2, 2500 U/ml), IL-4 (1280 U/ml), interferon-gamma (IFN-gamma; 100 U/ml), and granulocyte-macrophage colony-stimulating factor (GM-CSF; 50 U/ml). Neither tumor necrosis factor nor transforming growth factor beta (TGF-beta) was detected. Each of the cytokines present in EL-4 fluids was assessed for capacity to activate macrophages for destruction of parasites or to suppress intracellular killing. IFN-gamma and GM-CSF both activated macrophages to kill Leishmania; IL-2 and IL-4 had no activity for induction of this antimicrobial effector function. IL-2 and IL-4 were tested for their capacity to inhibit lymphokine- or IFN-gamma-induced destruction of L. major by macrophages: IL-4 was ineffective, but IL-2 markedly suppressed the activation of macrophages for intracellular killing. Addition of > or = 10 U/ml of IL-2 at the time of infection, or up to 4 h before, blocked up to 100% of the capacity of activated macrophages to kill intracellular amastigotes. Immunoaffinity treatment of EL-4 fluids with anti-IL-2 antibody resulted in > 80% reduction in suppression of intracellular killing. The suppressive effects of IL-2 were not direct, but mediated by TGF-beta. IL-2 induced resident peritoneal macrophages to secrete > 5000 pg/ml TGF-beta 1, a quantity that is > 500-fold higher than constitutive background levels (20-40 pg/ml) and is sufficient to block intracellular killing activities. This increase in secretion of TGF-beta was not dependent increases in TGF-beta 1 mRNA. Treatment of cultures with EL-4 fluids or recombinant IL-2 in the presence of antibody to TGF-beta 1 blocked the suppressive activity of both. Thus, IL-2 was the major suppressor factor in EL-4 fluids, and it acted indirectly through the induction and autocrine action of TGF-beta.
authors.affiliation: Department of Cellular Immunology, Walter Reed Army Institute of Research, Washington, DC.
authors.forename: B J
authors.initials: BJ
authors.lastname: Nelson
authors.forename: D
authors.initials: D
authors.lastname: Danielpour
authors.forename: J L
authors.initials: JL
authors.lastname: Rossio
authors.forename: J
authors.initials: J
authors.lastname: Turpin
authors.forename: C A
authors.initials: CA
authors.lastname: Nacy
mesh_terms: D000818:Animals; D007371:Interferon-gamma / Q000494:pharmacology; D007376:Interleukin-2 / Q000494:pharmacology*; D018320:Leishmania major / Q000276:immunology; D008262:Macrophage Activation / Q000187:drug effects*; D008264:Macrophages / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D015375:Receptors, Interleukin-2 / Q000032:analysis; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000096:biosynthesis*; D014407:Tumor Cells, Cultured
chemical_list: D007376:Interleukin-2; D015375:Receptors, Interleukin-2; D016212:Transforming Growth Factor beta; D007371:Interferon-gamma; D013755:Tetradecanoylphorbol Acetate