Spontaneous decrease of CD14 cell surface expression in human peripheral blood monocytes ex vivo

In the continuous presence of bacterial lipopolysaccharide (LPS), the membrane-bound LPS receptor, CD14, exhibits a biphasic pattern of surface expression in monocytes ex vivo; an initial increase is followed by a later decrease. In the presence of LPS, ex vivo changes in monocytic CD14 cell surface expression have been consistently interpreted as the direct result of LPS exposure. There has been little consideration for the possibility of additional cell culture effects. Here, an experiment is presented to dissect the differences between LPS effects and cell culture effects on monocytic CD14 cell surface expression ex vivo. The results show that in monocytes from diluted whole blood cultures, CD14 surface expression is induced in LPS-treated samples but decreased in untreated samples. These observations suggest that the previously observed biphasic surface expression pattern of CD14 in long-term LPS-treated monocytes may be the result of a superposition of LPS-induced expression and spontaneous disappearance of CD14 from the plasma membrane. Further, these results illustrate the importance of taking cell culture conditions into account when analyzing monocyte expression of CD14.