title: Paclitaxel enhances macrophage IL-12 production in tumor-bearing hosts through nitric oxide.
abstract: Tumor-induced macrophages (Mphis) mediate immunosuppression, in part, through increased production of factors that suppress T cell responsiveness and underproduction of positive regulatory cytokines. Pretreatment of tumor-bearing host (TBH) Mphis with the anticancer agent paclitaxel (Taxol) partially reverses tumor-induced Mphi suppressor activity, suggesting that paclitaxel may restore TBH Mphi production of proimmune factors. Because paclitaxel demonstrates LPS-mimetic capabilities and increased production of the LPS-induced immunostimulatory cytokine IL-12 could account for enhanced T cell responsiveness, we investigated whether paclitaxel induces Mphi IL-12 production. Tumor growth significantly down-regulated Mphi IL-12 p70 production through selective dysregulation of IL-12 p40 expression. LPS stimulation failed to overcome tumor-induced dysregulation of p40 expression. In contrast, paclitaxel significantly enhanced both normal host and TBH Mphi IL-12 p70 production in vitro, although TBH Mphi IL-12 production was lower than that of similarly treated normal host Mphis. Paclitaxel enhanced p40 expression in a dose-dependent manner. Through reconstituted Mphi IL-12 expression, paclitaxel pretreatment relieved tumor-induced Mphi suppression of T cell alloreactivity. Blocking Mphi NO suppressed paclitaxel's ability to induce IL-12 production. This suggests that paclitaxel-induced activities may involve a NO-mediated autocrine induction pathway. Collectively, these data demonstrate that paclitaxel restores IL-12 production in the TBH and ascribe a novel immunotherapeutic component to the pleiotropic activities of NO. Through its capacity to induce IL-12 production, paclitaxel may contribute to the correction of tumor-induced immune dysfunction.
authors.affiliation: Department of Biology, Microbiology and Immunology Section, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
authors.forename: D W
authors.initials: DW
authors.lastname: Mullins
authors.forename: C J
authors.initials: CJ
authors.lastname: Burger
authors.forename: K D
authors.initials: KD
authors.lastname: Elgert
mesh_terms: D000276:Adjuvants, Immunologic / Q000494:pharmacology*; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D019281:Dimerization; D007108:Immune Tolerance / Q000187:drug effects; D018664:Interleukin-12 / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000737:chemistry / Q000502:physiology; D008213:Lymphocyte 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; D009569:Nitric Oxide / Q000502:physiology*; D017239:Paclitaxel / Q000494:pharmacology*; D012513:Sarcoma, Experimental / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology
chemical_list: D000276:Adjuvants, Immunologic; D000972:Antineoplastic Agents, Phytogenic; D018664:Interleukin-12; D009569:Nitric Oxide; D017239:Paclitaxel