Lipopolysaccharide induces interleukin-6 release from rat peritoneal macrophages in vitro: evidence for a novel mechanism.

Interleukin-6 (IL-6) is a cytokine involved in the terminal differentiation of B-cells, T-cell activation, and secretion of hepatic acute phase proteins. The production of IL-6 is regulated by many factors, including IL-1 and lipopolysaccharide (LPS). Because IL-6 may be an important contributor to the effects of LPS in inflammation and septic shock, we investigated the ability of LPS to induce IL-6 release from peritoneal macrophages (m phi) in vitro. M phi were isolated from male Long-Evans rats, and cultured in 96-well tissue culture plates at 1 x 10(5) cells/well in serum-free RPMI-1640 medium. Following a 2-hr attachment period, the cells were rinsed twice to remove the nonadherent cells. LPS (0.006-100 ng/ml) stimulated IL-6 release by six- to 12-fold during a 4 hr incubation. In contrast, IL-1 beta (0.006-100 ng/ml) had no effect. Because cyclooxygenase metabolites of arachidonic acid are increased by LPS, we determined the effects of indomethacin (a cyclooxygenase inhibitor) and CGS8515 (a 5-lipoxygenase inhibitor) on LPS-induced IL-6 release. Neither indomethacin (10 microM) nor CGS8515 (2.5 microM) had any effect on basal or LPS-induced IL-6 release. Very low concentrations of LPS (0.01-1,000 pg/ml) stimulated IL-6 by two- to threefold. Pertussis toxin (10 ng/ml), which inactivates Gi protein, had no effect on LPS-induced IL-6 release from mø. Thromboxane B2 (TXB2) concentrations were also elevated with as little as 0.1 pg/ml LPS; however, pertussis toxin inhibited LPS-stimulated TXB2 release.(ABSTRACT TRUNCATED AT 250 WORDS)