Involvement of Toll-like receptor in silica-induced tumor necrosis factor alpha release from human macrophage cell line

Abstract

To characterize the role of Toll-like receptor 4 (TLR4) in silica-induced production of tumor necrosis factor alpha (TNFalpha) from macrophage cell line. The human macrophage cell line THP-1 was incubated with silica suspension. Cell media were collected and TNFalpha levels in the supernatants measured with ELISA. To examine the involvement of TLR4 in silica-induced TNFalpha release, the neutralizing antibody (HTA125) against human TLR4 receptor was employed to pretreat THP-1 cells prior to silica treatment. Moreover, murine macrophages expressing wild type or mutated TLR4 were also treated with silica to verify the effect of TLR4 in silica-induced TNFalpha release. Compared with the control group [(3.18 +/- 0.41) pg/ml], the TNFalpha release in cells exposed to 100 microg/ml silica for 4 h and 8 h [(4.71 +/- 0.84), (6.22 +/- 0.58) pg/ml, respectively] increased 1.48 and 1.96 fold, respectively. Pretreatment of THP-1 cells with 20 microg/ml HTA125 antibody significantly blocked silica-induced TNFalpha release by 27%. Furthermore, the TNFalpha content released from cells expressing mutated TLR4 reduced by 30% in compared with that from the cells expressing wild type TLR4 after silica stimulation. TLR4 mediates silica-induced TNFalpha release from macrophages.