Pretreatment of Low-Dose and Super-Low-Dose LPS on the Production of<i>In Vitro</i>LPS-Induced Inflammatory Mediators

Abstract

Pretreatment of low-dose lipopolysaccharide (LPS) induces a hyporesponsive state to subsequent secondary challenge with high-dose LPS in innate immune cells, whereas super-low-dose LPS results in augmented expression of pro-inflammatory cytokines. However, little is known about the difference between super-low-dose and lowdose LPS pretreatments on immune cell-mediated inflammatory and hepatic acute-phase responses to secondary LPS. In the present study, RAW 264.7 cells, EL4 cells, and Hepa-1c1c7 cells were pretreated with super-low-dose LPS (SL-LPS: 50 pg/mL) or low-dose LPS (L-LPS: 50 ng/mL) in fresh complete medium once a day for 2~3 days and then cultured in fresh complete medium for 24 hr or 48 hr in the presence or absence of LPS (1~10 g/mL) or concanavalin A (Con A). SL-LPS pretreatment strongly enhanced the LPS-induced production of tumor necrosis factor (TNF)-, interleukin (IL)-6, TNF-/IL-10, prostaglandin E2 (PGE 2 ), and nitric oxide (NO) by RAW 264.7 cells compared to the control, whereas L-LPS increased IL-6 and NO production only. SL-LPS strongly augmented the Con A-induced ratios of interferon (IFN)-/IL-10 in EL4 cells but decreased the LPS-induced ratios of IFN-/IL-10 compared to the control, while L-LPS decreased the Con A-and LPS-induced ratios of IFN-/IL-10. SL-LPS enhanced the LPS-induced production of IL-6 by Hepa1c1c-7 cells compared to the control, while L-LPS increased IL-6 but decreased IL-1 and C reactive protein (CRP) levels. SL-LPS pretreatment strongly enhanced the LPS-induced production of TNF-, IL-6, IL-10, PGE 2 , and NO in RAW 264.7 cells, and the IL-6, IL-1, and CRP levels in Hepa1c1c-7 cells, as well as the ratios of IFN-/IL-10 in LPS-and Con A-stimulated EL4 cells compared to L-LPS. These findings suggest that pre-conditioning of SL-LPS may contribute to the mortality to secondary infection in sepsis rather than pre-conditioning of L-LPS.