Leukotriene B4 up-regulates IL-6 rather than IL-1 synthesis in human monocytes.

Leukotriene B4 (LTB4) preferentially induced IL-6 mRNA accumulation and IL-6 protein release as assessed by ELISA and the B9 cell bioassay. In contrast, minimal IL-1 mRNA or protein was induced by LTB4 either in the absence or presence of muramyl dipeptide. Supernatants of LTB4-treated monocytes consistently showed enhanced thymocyte costimulatory activity and this was abrogated by 75-80% by anti-IL-1 antibody. Baseline production of IL-1 appeared however to be sufficient for a synergistic stimulation of thymocytes in the presence of IL-6. Our results now help clarify that LTB4 stimulated preferentially IL-6 production and that the observed LTB4-induced augmentation in thymocyte responses to monocyte supernatants is due to augmented IL-6 contents in the presence of baseline minimal IL-1 production.