The Effects of Interferon-γ and Bacterial Lipopolysaccharide on CD14 Expression in Human Monocytes

CD14 has been reported to be the lipopolysaccharide (LPS)-LPS binding protein receptor. The effects of interferon-γ (IFN-γ) on CD14 expression have not been clearly established. The purpose of this investigation was to examine the effects of IFN-γ alone and IFN-γ followed by bacterial LPS on CD14 expression. Human peripheral blood monocytes were isolated by counterflow centrifugal elutriation (CCE). Monocytes were cultured for 48 h with IFN-γ alone or for 24 h with IFN-γ followed by LPS for a second 24 h. IFN-γ alone caused a down-regulation of CD14 expression, as assessed by flow cytometry, relative to CD14 expression in untreated monocytes. In addition, CD14 expression was even more significantly down-regulated after IFN-γ pretreatment followed by either Prevotella intermedia or Salmonella typhimurium LPS. Likewise, the percentage of CD14⁺ monocytes decreased after IFN-γ alone and even more dramatically after IFN-γ treatment followed by either LPS. This study clearly demonstrated that IFN-γ down-regulates CD14 expression and that LPS following IFN-γ pretreatment potentiates this effect.