We investigated the effects of Th2 cell-associated cytokines, IL-4, IL-10, and IL-13, on prostaglandin (PG) production by human peripheral blood monocytes (HPBM) in terms of four parameters: PGE2 synthesis; cyclooxygenase activity; protein; and mRNA of two cyclooxygenase isozymes (cyclooxygenase-1 and cyclooxygenase-2). LPS-stimulated PGE2 synthesis and cyclooxygenase activity were suppressed by IL-4, IL-10, or IL-13. Furthermore, the LPS-dependent increase of cyclooxygenase activity in HPBM was attributable to cyclooxygenase-2 because it was inhibited by NS-398 (a cyclooxygenase-2-specific inhibitor). Western and Northern blot analyses revealed that the LPS-induced increases in cyclooxygenase-2 protein and mRNA were attenuated by the addition of IL-4, IL-10, or IL-13. In contrast, cyclooxygenase-1 protein and mRNA were hardly detected in monocytes that were incubated with or without LPS in the presence or absence of IL-4, IL-10, and IL-13. These results suggest that the reduction of LPS-induced PGE2 synthesis and cyclooxygenase activity by IL-4, IL-10, and IL-13 in HPBM are mainly due to the down-regulation of cyclooxygenase-2 selectively induced by LPS. Conversely, IFN-gamma, a Th1 cell-associated cytokine, did not affect PGE2 production and cyclooxygenase activity. These data suggest a mechanism for modulation of inflammation by the anti-inflammatory Th2 cell-associated cytokines but not a Th1 cell-associated cytokine.

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