Lipopolysaccharide upregulates surface expression of CD14 on human alveolar macrophages

This study was undertaken to examine the surface expression and regulation of CD14 on human alveolar macrophages (HAM). HAM obtained by bronchoalveolar lavage were cultured with or without LPS and with or without fetal bovine serum (FBS) on plastic or Teflon surfaces. CD14 expression was assessed by immunofluorescence. The roles of protein tyrosine kinase, protein kinase A, and protein kinase C were also evaluated utilizing inhibitors of these enzymes. HAM expressed very low levels of surface CD14 at baseline. CD14 was upregulated on HAM with time in culture in the presence of FBS and/or LPS; adherence did not affect CD14 expression. Inhibitors of protein kinase C and protein tyrosine kinase prevented the upregulation of CD14 by LPS but did not effect the upregulation of CD14 by FBS. These studies show that LPS can upregulate expression of its receptor on HAM and that this effect is accentuated by serum-derived factors.