CD14 AND CD11B MEDIATE SERUM-INDEPENDENT BINDING TO HUMAN MONOCYTES OF AN ACYLPOLYGALACTOSIDE ISOLATED FROM KLEBSIELLA-PNEUMONIAE

A water-soluble acylpolygalactosyl (APG) of 34 kDa was obtained from t he Klebsiella pneumoniae membrane by alkaline hydrolysis and delipidat ion. APG comprises a poly(1,3)galactose chain, a core, and a lipid moi ety made of a glucosamine disaccharide with two N-linked beta OH-myris tates. The monocyte binding sites for APG were investigated by flow cy tometry. Biotin-labelled APG (Biot-APG) bound to monocytes at 4 degree s C in the absence of serum, calcium, and magnesium. The binding was d ose dependent, saturable, and displaced by unlabelled APG. Neither the polysaccharide chain present in APG-related molecules nor the PP1 gro up or additional ester-linked myristates and palmitates were required- for APG binding. The role of CD11b and CD14 was demonstrated by compet itive inhibition with monoclonal antibodies and by the uptake of APG b y these solubilized proteins. APG was rapidly internalized into monocy tes at 37 degrees C while CD14 and CD11b/CD18 molecules were partially down-modulated. Lipopolysaccharides (LPS) from the same K. pneumoniae strain and from Escherichia coli and Salmonella minnesota partially c ompeted for Biot-APG binding in the absence but not in the presence of serum. When altered by alkaline hydrolysis, those LPS became strong c ompetitors for APG binding. It was concluded that alkaline hydrolysis of the K. pneumoniae membrane yielded molecules structurally related t o LPS which bind to LPS membrane receptors in the absence of serum.