Interleukin-6 after LPS decreases macrophage tumor necrosis factor-alpha production

Introduction. Elevated serum levels of Interleukin-6 (IL-6) correlate with multiple organ dysfunction syndrome (MODS) and mortality in critically ill patients. Data from animal models of shock and sepsis suggest that exogenous IL-6 protects against inflammation. We hypothesized that IL-6 pretreatment down regulates macrophage cytokine production. Our objective was to investigate the timing of IL-6 administration on TNF-α production from the macrophage. Methods. Differentiated THP-1 macrophages were divided into 10 groups: (1, 2) Control-6 and -24 (controls harvested at 6 and 24 h); (3, 4) LPS-6 and LPS-24 (LPS for 6 and 24 h); (5, 6) IL-6-6 and IL-6-24 (No LPS, IL-6 treatment for 1 h then incubation for 6 and 24 h); (7, 8) LPS + IL-6-6 and LPS + IL-6-24 (LPS for 6 and 24 h then IL-6 treatment for 1 h; (9, 10) IL-6 + LPS-6 and IL-6 + LPS-24 (pretreated with IL-6 for 1 h, then LPS for 6 and 24 h). Concentrations of LPS were 100 ng/ml and IL-6 1000 U/ml. Total RNA was isolated and TNF-α gene expression performed using Q-RT-PCR (Qiagen RNeasy Kit, Valencia, CA, and MX3000P, Stratagene, La Jolla, CA). Supernatants were assayed for TNF-α by ELISA (R&D Systems, Minneapolis, MN). Data were analyzed by ANOVA (Primer vs. 3.0). Results. Compared to controls, IL-6 alone, and IL-6 after LPS, LPS and IL-6 pretreatment + LPS increased TNF-α mRNA levels ( P = 0.002). mRNA levels from LPS and IL-6 + LPS were similar at 6 h (552 ± 59 and 441.5 ± 98) and 24 h (84 ± 1 and 88 ± 9) ( P = 0.43). Conclusion. IL-6 pretreatment did not alter TNF-alpha levels. Surprisingly, IL-6 administration after LPS decreased TNF-α mRNA and protein. This data suggest that IL-6 does not decrease cytokine production via preconditioning. Further study is needed to elucidate the mechanism by which IL-6 treatment after LPS decreases TNF-α. FIG. 1 Compared to LPS and IL-6 + LPS, LPS + IL-6 decreased TNF-α mRNA at both 6 (117 ± 1; P = 0.002) and 24 h (53 ± 11; P = 0.000). TNF-α protein levels mirrored mRNA data; P = 0.000.