Comparison of SP-A and LPS effects on the THP-1 monocytic cell line

Surfactant protein A (SP-A) increases production of proinflammatory cytokines by monocytic cells, including THP-1 cells, as does lipopolysaccharide (LPS). Herein we report differences in responses to these agents. First, polymyxin B inhibits the LPS response but not the SP-A response. Second, SP-A-induced increases in tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-8 are reduced by >60% if SP-A is preincubated with Survanta (200 μg/ml) for 15 min before addition to THP-1 cells. However, the LPS effects on TNF-α and IL-8 are inhibited by <20% and the effect on IL-1β by <50%. Third, at Survanta levels of 1 mg/ml, SP-A-induced responses are reduced by >90%, and although the inhibitory effects on LPS action increase, they still do not reach those seen with SP-A. Finally, we tested whether SP-A could induce tolerance as LPS does. Pretreatment of THP-1 cells with LPS inhibits their response to subsequent LPS treatment 24 h later, including TNF-α, IL-1β, and IL-8. Similar treatment with SP-A reduces TNF-α, but IL-1β and IL-8 are further increased by the second treatment with SP-A rather than inhibited as with LPS. Thus, whereas both SP-A and LPS stimulate cytokine production, their mechanisms differ with respect to inhibition by surfactant lipids and in ability to induce tolerance.