title: Reciprocal CD40 signals through p38MAPK and ERK-1/2 induce counteracting immune responses.
abstract: Macrophages play host to Leishmania major, a parasite that causes leishmaniasis in 500,000 people annually. Macrophage-expressed CD40, a costimulatory molecule, induces interleukin-12 (IL-12)-dependent and interferon-gamma (IFN-gamma)-dependent host-protective immune responses to Leishmania and other intracellular pathogens. Paradoxically, IL-10, another CD40-induced cytokine in macrophages, promotes Leishmania infection. How CD40 signaling regulates the secretion of these two counteractive cytokines remains unknown. Here we show that weak CD40 signals induce extracellular stress-related kinase-1/2 (ERK-1/2)-dependent IL-10 expression, whereas stronger signals induce p38 mitogen-activated protein kinase (p38MAPK)-dependent IL-12 production. p38MAPK and ERK-1/2 therefore have counter-regulatory actions. Leishmania skews CD40 signaling toward ERK-1/2, inducing IL-10, which inhibits activation of CD40-induced p38MAPK and expression of inducible nitric oxide synthase-2 (iNOS-2) and IL-12. ERK-1/2 inhibition or IL-10 neutralization restores CD40-induced p38MAPK activation and parasite killing in macrophages and the BALB/c mouse, a susceptible host. These data uncover a new immune evasion strategy, whereby Leishmania differentially modulates CD40-engaged, reciprocally functioning signaling modules, and provide a new conceptual framework for immune homeostasis.
authors.affiliation: National Centre for Cell Science, Ganeshkhind, Pune 411007, India.
authors.forename: Ram Kumar
authors.initials: RK
authors.lastname: Mathur
authors.forename: Amit
authors.initials: A
authors.lastname: Awasthi
authors.forename: Pallavi
authors.initials: P
authors.lastname: Wadhone
authors.forename: B
authors.initials: B
authors.lastname: Ramanamurthy
authors.forename: Bhaskar
authors.initials: B
authors.lastname: Saha
mesh_terms: D000818:Animals; D019013:CD40 Antigens / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D018320:Leishmania major / Q000276:immunology* / Q000472:pathogenicity*; D020935:MAP Kinase Signaling System; D017737:Macrophages, Peritoneal / Q000201:enzymology / Q000276:immunology / Q000469:parasitology; D051379:Mice; D008807:Mice, Inbred BALB C; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D019013:CD40 Antigens; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases