CD14 is expressed and released as soluble CD14 by human intestinal epithelial cells in vitro: Lipopolysaccharide activation of epithelial cells revisited

Human endothelial as well as epithelial cells were shown to respond to lipo polysaccharides (LPSs). However, the expression and release of CD14 by thes e so-called CD14-negative cells have not been studied in detail. We investi gated three human intestinal epithelial cell lines (ECLs), SW-480, HT-29, a nd Caco-2, for their expression of CD14 and CD11c/CD18 as well as their res ponsiveness to endotoxins. Fluorescence-activated cell sorter analysis reve aled no expression of CD11c/CD18, but there was low expression of membrane- bound CD14 on HT-29, Caco-2, and SW-480 ECLs. Both Western blotting and rev erse transcription-PCR confirmed the CD14 positivity of all three intestina l ECLs. No substantial modulation of CD14 expression was achieved after 6, 8, 18, 24, and 48 h of cultivation with 10-fold serial dilutions of LPS ran ging from 0.01 ng/ml to 100 mug/ml. Interestingly, soluble CD14 was found i n the tissue culture supernatants of all three ECLs. Finally, only HT-29 an d SW-4801 and not Caco-21 cells; responded to LPS exposure (range, 0.01 ng/ ml to 100 mug/ml) by interleukin 8 release. Thus, we show that HT-29, SW-48 0, and Caco-2 human intestinal ECLs express membrane-bound CD14. As Caco-2 cells did not respond to LPS, these cell lines might be an interesting mode l for studying the receptor complex for LPS. The fact that human intestinal epithelial cells are capable not only of expression but also of release of soluble CD14 may have important implications in vivo, e.g., in shaping the interaction between the mucosal immune system and bacteria in the gut and/ or in the pathogenesis of endotoxin shock.