Involvement of CD14 in lipopolysaccharide-induced tumor necrosis factor-alpha, IL-6 and IL-8 release by human monocytes and alveolar macrophages.

CD14 has been reported to function as a receptor for bacterial LPS complexed with serum proteins, transducing an activation signal for TNF-alpha production. We found that the anti-CD14 mAb MEM-18 inhibited not only LPS-induced release of TNF-alpha, but also LPS-induced, TNF-alpha independent release of IL-6 and IL-8 by human monocytes and alveolar macrophages. Inhibitory effect of MEM-18 was detected both in the presence of human or bovine calf serum and under serum-free conditions. In contrast, MEM-18 did not block release of these cytokines induced by IL-1 beta, TNF-alpha, PMA, and zymosan. We conclude that CD14 is involved in LPS-induced release of TNF-alpha, IL-6, and IL-8 by monocytes and alveolar macrophages and that this receptor appears to be able to recognize LPS directly in the absence of serum.