Cytokine‐stimulated release of decay‐accelerating factor (DAF; CD55) from HT‐29 human intestinal epithelial cells
Expression of DAF (CD55) is enhanced on colonic epithelial cells of patients with ulcerative colitis (UC), and stool DAF concentrations are increased in patients with active disease. Cytokines are known to modulate DAF expression in various human cells, and lesions of UC reveal altered profiles of cytokine production. In this study, we evaluate the effects of various cytokines, IL‐1β, IL‐2, IL‐4, IL‐6, IL‐8, IL‐10, and interferon‐gamma (IFN‐γ), on the synthesis and kinetics of DAF protein in HT‐29 human intestinal epithelial cells. Using flow cytometry and an ELISA, we found that HT‐29 cells constitutively express DAF on the cell surface and spontaneously release DAF into the culture supernatant under standard culture conditions. When the culture supernatant was centrifuged at 100 000 g, nearly a half of DAF was precipitated, indicating that one half of the released DAF was present as a membrane‐bound form and the other half as a soluble form. Analysis of the culture supernatant of biotin surface‐labelled HT‐29 cells suggested that the soluble form DAF was derived by secretion from within the cell or by cleavage from the cell surface. Among the cytokines, IL‐4 markedly, and IL‐1β moderately, enhanced the expression and the release of DAF. Actinomycin D, cycloheximide, and brefeldin A inhibited the increase in DAF release induced by IL‐4 and IL‐1β stimulation. These results suggest that DAF is released from intestinal epithelial cells in response to cytokine stimulation and that IL‐4 and IL‐1β are possible cytokines involved in DAF release into the colonic lumen of patients with UC.