Binding of lipopolysaccharide (LPS) to CHO cells does not correlate with LPS-induced NF-chi B activation

Activation of myeloid cells by lipopolysaccharide (LPS) is a key event in t he development of gram-negative sepsis. One crucial step within this proces s is the binding of LPS to CD14. CD14 is a glycosylphosphatidylinositol (GP I)-anchored membrane protein requiring at least one additional membrane-spa nning molecule for signal transduction. It is not clear whether the functio n of CD14 is to merely catalyze LPS binding, followed by the interaction of LPS with the signal transducer, or whether CD14 has a more specific functi on and may be a part of the signaling complex. To address this question we generated Chinese hamster ovary (CHO) cells expressing a human GPI-anchored form of LPS-binding protein (mLBP) to substitute for CD14 as LPS acceptor molecule. By comparison of CHO/mLBP with CHO/vector and CHO/CD14 cells we f ound that expression of GPI-linked LBP results in an enhanced binding of LP S but not in an increase in cell activation as determined by translocation of NF-kappa B. Furthermore, excess of recombinant soluble LBP resulted also in increased LPS binding without affecting NF-kappa B translocation. These data show that LPS binding alone is not sufficient to induce signaling. We conclude that CD14 is more than a catalyst for LPS binding: it seems to be directly involved in LPS signaling and thus appears to be an essential par t of the signaling complex.