title: Leishmania mexicana promastigotes inhibit macrophage IL-12 production via TLR-4 dependent COX-2, iNOS and arginase-1 expression.
abstract: The effects of Leishmania mexicana metacyclic promastigotes upon MAP kinase signalling in mouse bone marrow macrophages and subsequent expression of the disease regulatory proteins iNOS and COX-2 were studied. At a ratio of 5:1, promastigotes caused a marked increase in phosphorylation of the three major MAP kinases, ERK, p38 and JNK. MAP kinase signalling was substantially reduced in TLR-4(-/-) but not TLR-2(-/-) deficient macrophages and completely abolished in double TLR-2/4(-/-) macrophages. A similar outcome was observed using cysteine peptidase B deficient amastigotes. Furthermore, whilst promastigotes had no independent effect on iNOS or COX-2 expression, they prolonged the induction of these proteins stimulated by LPS and enhanced PGE(2) and NO production. Induction of COX-2 and iNOS was also TLR-4 dependent. Blockade of either PGE(2) or NO production with indomethacin or l-NAME reversed promastigote inhibition of LPS induced IL-12 production. Promastigotes also increased macrophage arginase-1 expression and enhanced arginase activity, both of which were substantially reduced in TLR-4 but not TLR-2 deficient macrophages. Surprisingly, arginase inhibition by Nor-NOHA also caused a reversal of promastigote mediated inhibition of macrophage IL-12 production. These data demonstrate for the first time the role of TLR-4 in mediating the effects of L. mexicana promastigotes on MAP kinase activation, up-regulation of COX-2, iNOS as well as arginase-1 expression in macrophages and further shows that PGE(2), NO and arginase activity all contribute substantially to the inhibition of host cell IL-12 production.
authors.affiliation: Division of Physiology & Pharmacology, Strathclyde Institute for Pharmacy & Biomedical Sciences, 27 Taylor Street, Glasgow G4 0NR, UK.
authors.forename: Muhannad
authors.initials: M
authors.lastname: Shweash
authors.forename: H
authors.initials: H
authors.lastname: Adrienne McGachy
authors.forename: Juliane
authors.initials: J
authors.lastname: Schroeder
authors.forename: Thikryat
authors.initials: T
authors.lastname: Neamatallah
authors.forename: Clare E
authors.initials: CE
authors.lastname: Bryant
authors.forename: Owain
authors.initials: O
authors.lastname: Millington
authors.forename: Jeremy C
authors.initials: JC
authors.lastname: Mottram
authors.forename: James
authors.initials: J
authors.lastname: Alexander
authors.forename: Robin
authors.initials: R
authors.lastname: Plevin
mesh_terms: D000818:Animals; D001119:Arginase / Q000096:biosynthesis / Q000276:immunology; D015153:Blotting, Western; D051546:Cyclooxygenase 2 / Q000096:biosynthesis / Q000276:immunology; D004789:Enzyme Activation / Q000276:immunology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000276:immunology / Q000378:metabolism; D018664:Interleukin-12 / Q000096:biosynthesis* / Q000276:immunology; D007894:Leishmania mexicana / Q000276:immunology; D007896:Leishmaniasis / Q000276:immunology* / Q000378:metabolism; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology; D051379:Mice; D052247:Nitric Oxide Synthase Type II / Q000096:biosynthesis / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology; D051197:Toll-Like Receptor 4 / Q000276:immunology / Q000378:metabolism*
chemical_list: C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D018664:Interleukin-12; D052247:Nitric Oxide Synthase Type II; D051546:Cyclooxygenase 2; D048049:Extracellular Signal-Regulated MAP Kinases; C544448:Arg1 protein, mouse; D001119:Arginase