Phagocytosis of gram-negative bacteria by a unique CD14-dependent mechanism.
THP-1-derived cell lines were stably transfected with constructs encoding glycophosphatidylinositol (GPI)-anchored or transmembrane forms of human CD14. CD14 expression was associated with enhanced phagocytosis of serum (heat-inactivated)-opsonized Escherichia coli (opEc). Both the GPI-anchored and transmembrane forms of CD14 supported phagocytosis of opEc equally well. Lipopolysaccharide-binding protein (LBP) played a role in CD14-dependent phagocytosis as evidenced by inhibition of CD14-dependent phagocytosis of opEc with anti-LBP monoclonal antibody (mAb) and by enhanced phagocytosis of E. coli opsonized with purified LBP. CD14-dependent phagocytosis was inhibited by a phosphatidylinositol (PI) 3-kinase inhibitor (wortmannin) and a protein tyrosine kinase inhibitor (tyrphostin 23) but not a protein kinase C inhibitor (bisindolyl-maleimide) or a divalent cation chelator (ethylenediaminetetraacetate). Anti-LBP mAb 18G4 and anti-CD14 mAb 18E12 were used to differentiate between the pathways involved in CD14-dependent phagocytosis and CD14-dependent cell activation. F(ab')2 fragments of 18G4, a mAb to LBP that does not block cell activation, inhibited ingestion of opEc by THP1-wtCD14 cells. 18E12 (an anti-CD14 mAb that does not block LPS binding to CD14 but does inhibit CD14-dependent cell activation) did not inhibit phagocytosis of LBP-opEc by THP1-wtCD14 cells. Furthermore, CD14-dependent phagocytosis was not inhibited by anti-CD18 (CR3 and CR4 beta-chain) or anti-Fcgamma receptor mAb.
Schiff
D E
DE
Department of Immunology, The Scripps Research Institute, La Jolla, California 92037, USA.
Kline
L
L
Soldau
K
K
Lee
J D
JD
Pugin
J
J
Tobias
P S
PS
Ulevitch
R J
RJ
D002460:Cell Line; D004926:Escherichia coli / Q000502:physiology*; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D009000:Monocytes / Q000382:microbiology* / Q000502:physiology*; D010587:Phagocytosis / Q000502:physiology*
D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides