Synthesis and surface expression of CD14 by human endothelial cells

Previous studies have reported that human vascular enitothelial cells lack the membrane-bound lipopolysaccharide (LPS) receptor, CD14 (mCD14). By opti mizing assay conditions, including the selection of anti-CD14 monoclonal an tibody, we now demonstrate that human umbilical vein endothelial cells (HUV EC) express CD14 on the cell surface. Single-passage HUVEC showed approxima tely 20 times less expression of CD14 than monocytes, Interestingly, there was significant loss of surface CD14 expression with increasing numbers of culture passages. Evidence for synthesis of CD14 by HUVEC was provided by t he finding that L-[S-35]methionine was incorporated into CD14, In addition, the expression of CD14 on HUVEC was upregulated by LPS, lysophosphatidic a cid, and tissue culture supplements, and this upregulation was dependent on protein synthesis. Furthermore, the results imply that mCD14 is required f or LPS-induced activation of endothelial cells in the absence of serum and that it acts in concert with serum factors (soluble CD14), Our results prov ide evidence that CD14 is expressed by endothelial cells and suggest that t he previous inability to observe expression of this molecule has been due t o culture and staining conditions. This finding has important implications for the understanding of the mechanisms by which LPS stimulates endothelial cells and the management of sepsis caused by gram-negative bacteria.