Important role of membrane-associated CD14 in the induction of IFN-beta and subsequent nitric oxide production by murine macrophages in response to bacterial lipopolysaccharide.

The surface antigen CD14 is known to play a central role in the recognition of lipopolysaccharide by macrophages. We characterized a mutant cell line, J7.DEF.3, derived from a murine macrophage-like cell line, J774.1, to be defective in the ability to express the membrane-associated form of CD14 (mCD14) but not in the ability to release the soluble form of CD14 (sCD14), and used these parent and mutant cells to investigate the role of CD14 in lipopolysaccharide signaling. In response to lipopolysaccharide stimulation, mutant cells produced slightly less tumor necrosis factor than parent cells, and produced much less (negligible level) nitric oxide than parent cells. Production of both tumor necrosis factor and nitric oxide by parent cells upon lipopolysaccharide stimulation was suppressed by anti-CD14 serum. Expression of interferon-beta mRNA by stimulation with lipopolysaccharide, detected in parent cells, was barely detectable in mutant cells and in enzymatically mCD14-eliminated parent cells. Lipopolysaccharide-induced nitric oxide production in parent cells was suppressed by anti-(murine interferon-beta), and its production in the mutant cells appeared and increased dose dependently on exogenously supplied murine interferon-beta in the presence of lipopolysaccharide. These results provide new insight into the lipopolysaccharide signaling pathway, indicating that the lipopolysaccharide signal for interferon-beta production is transduced through a mCD14-dependent pathway and that the endogenously generated interferon-beta is an essential cofactor leading to nitric oxide production. Nuclear translocation of a transcription factor, nuclear factor kappaB, was observed in both parent and mutant cells following stimulation with a low dose of lipopolysaccharide, and mitogen-activated protein kinases were also activated in both types of cell, although a higher dose of lipopolysaccharide was required by the mutant cells than by the parent cells. These results indicate that these signaling factors may participate in the mCD14-independent lipopolysaccharide signaling pathway rather than in the mCD14-dependent interferon-beta-producing pathway.