LIPOPOLYSACCHARIDE IN COMBINATION WITH SERUM POTENTIATES THE STIMULATED ACTIVITY OF PHOSPHOLIPASE-D IN HUMAN NEUTROPHILS VIA CD14

The addition of fMet-Leu-Phe or phorbol 12-myristate 13-acetate to hum an neutrophils stimulates phospholipase D activity as evidenced by the release of phosphatidic acid and the generation of diacylglycerol, an d in the presence of ethanol the formation of phosphatidyl ethanol. Th e activation of phospholipase D by either the chemotactic factor or ac tive phorbol ester is inhibited by the tyrosine kinase inhibitor erbst atin. The fMet-Leu-Phe-induced stimulation of this enzyme is greatly p otentiated in cells which have been preincubated with low concentratio ns of lipopolysaccharide and serum. The presence of serum is essential for the potentiation by low concentrations of lipopolysaccharide. Mor eover, the monoclonal antibody MY4(IgG2b) against CD14 inhibits the po tentiation by the low concentration of lipopolysaccharide. These data suggest three important points. First, a tyrosine kinase step is neces sary for the activation of phospholipase D. This suggests that the pho spholipase D enzyme needs to be phosphorylated on tyrosine residues to be activated. Second, low concentrations of lipopolysaccharide, in th e presence of serum, can potentiate the stimulated activity of this en zyme. Third, the priming action of the lipopolysaccharide-serum comple x is mediated by CD14.