Monocyte antigen CD14 is a phospholipid anchored membrane protein

A cDNA clone encoding the human monocyte antigen CD14 was isolated by transient expression in COS cells of a cDNA library prepared from phorbol diester-treated HL60 cells. RNA blot analysis showed abundant expression of a single mRNA species in mature monocytes and an increased expression of the mRNA following induction of differentiation in leukemic cell lines. The DNA blot hybridization pattern was consistent with a single-copy gene. The predicted amino acid sequence lacks the characteristic transmembrane domain and stop transfer motif of conventionally anchored membrane proteins. COS cells transfected with the CD14 cDNA released virtually all CD14 protein in soluble form following treatment with glycosyl phosphatidylinositol-specific phospholipase C, and CD14 immunoreactivity was absent from the affected monocytes of a patient with paroxysmal nocturnal hemoglobinuria (PNH). The data show that, to the limit of experimental sensitivity, all monocyte CD14 is joined to the plasma membrane by a phosphatidylinositol phospholipid.