Paclitaxel Enhances Macrophage IL-12 Production in Tumor-Bearing Hosts Through Nitric Oxide

Tumor-induced macrophages (Mφs) 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) Mφs with the anticancer agent paclitaxel (Taxol) partially reverses tumor-induced Mφ suppressor activity, suggesting that paclitaxel may restore TBH Mφ 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 Mφ IL-12 production. Tumor growth significantly down-regulated Mφ 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 Mφ IL-12 p70 production in vitro, although TBH Mφ IL-12 production was lower than that of similarly treated normal host Mφs. Paclitaxel enhanced p40 expression in a dose-dependent manner. Through reconstituted Mφ IL-12 expression, paclitaxel pretreatment relieved tumor-induced Mφ suppression of T cell alloreactivity. Blocking Mφ 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.

IL-18 Promotes Type 1 Cytokine Production from NK Cells and T Cells in Human Intracellular Infection

We investigated the role of IL-18 in leprosy, a disease characterized by polar cytokine responses that correlate with clinical disease. In vivo, IL-18 mRNA expression was higher in lesions from resistant tuberculoid as compared with susceptible lepromatous patients, and, in vitro, monocytes produced IL-18 in response to Mycobacterium leprae. rIL-18 augmented M. leprae-induced IFN-γ in tuberculoid patients, but not lepromatous patients, while IL-4 production was not induced by IL-18. Anti-IL-12 partially inhibited M. leprae-induced release of IFN-γ in the presence of IL-18, suggesting a combined effect of IL-12 and IL-18 in promoting M. leprae-specific type 1 responses. IL-18 enhanced M. leprae-induced IFN-γ production rapidly (24 h) by NK cells and in a more sustained manner (5 days) by T cells. Finally, IL-18 directly induced IFN-γ production from mycobacteria-reactive T cell clones. These results suggest that IL-18 induces type 1 cytokine responses in the host defense against intracellular infection.