Surfactant protein A regulates cytokine production in the monocytic cell line THP-1

Surfactant lipids inhibit cytokine production by immune cells, and surfactant protein A (SP-A) stimulates it. By enzyme-linked immunosorbent assay and mRNA blotting, we studied proinflammatory cytokine production by the monocytic cell line THP-1. SP-A caused increases in tumor necrosis factor (TNF)-alpha within 1 h, peaking at 4 h and then declining. Interleukin (IL)-1 beta increased and stayed elevated for 24 h. SP-A stimulated IL-8 also, peaking at 4 h, rapidly declining, and peaking again at 24 h. SP-A-dependent changes were detected for IL-6, but at higher SP-A doses. mRNA levels for TNF-alpha and IL-1 beta increased in response to SP-A, peaking within 2 h. The increases in TNF-alpha mRNA and protein induced by SP-A were inhibited by surfactant lipids. For IL-1 beta and IL-8, the lipids either had no inhibitory influence or inhibited less than for TNF-alpha. This suggests that the ability of macrophages to participate in inflammatory reactions is enhanced by SP-A alone or by mixtures of lipids and SP-A containing more SP-A than in normal surfactant, as occurs in many conditions leading to inflammation.