SOLUBLE CD14 TRUNCATED AT AMINO-ACID-152 BINDS LIPOPOLYSACCHARIDE (LPS) AND ENABLES CELLULAR-RESPONSE TO LPS

CD14 is a 55-kDa glycoprotein which binds lipopolysaccharide (LPS) and enables LPS-dependent responses in a variety of cells. In order to id entify the domains in CD14 required for function, we deleted increasin g amounts of CD14 from the C terminus. Truncated CD14 cDNA sequences w ere transfected into COS-7 cells and serum-free conditioned medium was analyzed for mutant CD14 expression and bioactivity, Mutant CD14s con taining as few as 152 amino acids were found to have activity equivale nt to full-length sCD14, To further characterize the mutant CD14, we c onstructed a stable Chinese hamster ovary cell line expressing sCD14(1 -152) and purified the protein to homogeneity. sCD14(1-152) bound radi oactive LPS, enabled U373 cells to synthesize interleukin 6 in respons e to LPS, and enabled human neutrophils to respond to smooth LPS. In a ll of these assays, the behavior of sCD14(1-152) was quantitatively si milar to full-length sCD14. We also found that two neutralizing anti-C D14 antibodies (3C10 and MEM-18) bound and neutralized sCD14(1-152). W e conclude from these experiments that the N-terminal 152 amino acids of CD14 are sufficient to bind LPS and confer essentially wild-type bi oactivity in vitro.