BACKGROUND: CD14 was first described as a differentiation antigen on the surface of myeloid lineage cells. It acts as a glycosylphosphatidylinositol (GPI)-anchored receptor for the complex of lipopolysaccharide (LPS) and plays a key role in the activation of LPS-induced monocytes. The purpose of this study was to observe the expression of CD14 protein and its gene in the human U937 promonocytic cell line when these cells were exposed to 1,25-dihydroxyvitamin D3(VitD3) and investigate their sensitivity to endotoxin stimulation. 
METHODS: U937 cells were exposed to (0.1 μmol) VitD3 for 24 hours and were induced to express the CD14 mRNA gene and CD14 protein, then their responses were observed when they were stimulated with different concentrations of LPS for different time.
RESULTS: The U937 cells induced by VitD3 were found to stably express CD14 mRNA and CD14 protein. And CD14 protein enhanced the sensitivity of U937/CD14 cells to lipopolysaccharide (LPS) stimulation. NF-κB in U937/CD14 cells can be activated with low concentration of LPS (1 ng/ml-10 ng/ml), the TNF-α mRNA gene was induced, and then TNF-α was produced and released into the supernatant of culture.
CONCLUSION: VitD3 can induce U937 cell to express the CD14 gene and CD14 protein and enhance the response of this type of cells to LPS stimulation.