title: Leukocyte Ig-like receptor B4 (LILRB4) is a potent inhibitor of FcgammaRI-mediated monocyte activation via dephosphorylation of multiple kinases.
abstract: The leukocyte immunoglobulin-like receptor (LILR) B4 belongs to a family of cell surface receptors that possesses cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIMs). LILRB4 is believed to down-regulate activation signals mediated by non-receptor tyrosine kinase cascades through the recruitment of SHP-1. However, the exact mechanisms of LILRB4-mediated inhibition are not fully elucidated. In this study, we demonstrate high level surface expression of LILRB4 on THP-1 cells and primary peripheral blood monocytes, which profoundly inhibited production of a key pro-inflammatory cytokine (TNFalpha) induced by FcgammaRI (CD64). We also report that LILRB4 aggregated to sites of activation upon co-ligation with CD64 and that this may enhance its inhibitory effects. Cross-linking of CD64 on THP-1 cells markedly increased phosphorylation of multiple proteins including tyrosine kinases and signaling molecules (Lck, Syk, LAT, and Erk), an adaptor protein that targets protein-tyrosine kinases for degradation (c-Cbl) and a protein involved in the formation of actin cytoskeletal rearrangement (alpha-actinin-4). Co-ligation of LILRB4 considerably reduced CD64-mediated phosphorylation of Lck, Syk, LAT, Erk, and c-Cbl but not alpha-actinin-4, suggesting selective inhibition of signaling molecules. Treatment of cells with a broad-spectrum phosphatase inhibitor, sodium pervanadate (SP), significantly reversed LILRB4-mediated inhibition of TNFalpha production and protein tyrosine phosphorylation. In comparison, treatment with an SHP-1 specific inhibitor, sodium stibogluconate (SS) has no effects indicating involvement of phosphatase(s) other than SHP-1 in LILRB4 signaling. Collectively, our data show LILRB4 is a potent inhibitor of monocytes activation. This may provide a new potential therapeutic strategy for inflammatory conditions characterized by excessive TNFalpha production.
authors.affiliation: Centre for Infection and Inflammation Research, University of New South Wales, Sydney, New South Wales 2052, Australia.
authors.forename: Hao Kim
authors.initials: HK
authors.lastname: Lu
authors.forename: Carles
authors.initials: C
authors.lastname: Rentero
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Raftery
authors.forename: Luis
authors.initials: L
authors.lastname: Borges
authors.forename: Katherine
authors.initials: K
authors.lastname: Bryant
authors.forename: Nicodemus
authors.initials: N
authors.lastname: Tedla
mesh_terms: D000185:Actinin / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D018189:Immunomagnetic Separation; D008562:Membrane Glycoproteins; D051379:Mice; D009000:Monocytes / Q000166:cytology / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D017452:Receptors, IgG / Q000235:genetics / Q000378:metabolism*; D011971:Receptors, Immunologic; D015398:Signal Transduction / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: C111453:ACTN4 protein, human; D004791:Enzyme Inhibitors; C489017:FCGR1A protein, human; C107907:LILRB4 protein, human; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D017452:Receptors, IgG; D011971:Receptors, Immunologic; D014409:Tumor Necrosis Factor-alpha; D000185:Actinin; D011494:Protein Kinases