title: Intrinsic differences in the initiation of B cell receptor signaling favor responses of human IgG(+) memory B cells over IgM(+) naive B cells.
abstract: The acquisition of long-lived memory B cells (MBCs) is critical for the defense against many infectious diseases. Despite their importance, little is known about how Ags trigger human MBCs, even though our understanding of the molecular basis of Ag activation of B cells in model systems has advanced considerably. In this study, we use quantitative, high-resolution, live-cell imaging at the single-cell and single-molecule levels to describe the earliest Ag-driven events in human isotype-switched, IgG-expressing MBCs and compare them with those in IgM-expressing naive B cells. We show that human MBCs are more robust than naive B cells at each step in the initiation of BCR signaling, including interrogation of Ag-containing membranes, formation of submicroscopic BCR oligomers, and recruitment and activation of signaling-associated kinases. Despite their robust response to Ag, MBCs remain highly sensitive to FcγRIIB-mediated inhibition. We also demonstrate that in the absence of Ag, a portion of MBC receptors spontaneously oligomerized, and phosphorylated kinases accumulated at the membrane and speculate that heightened constitutive signaling may play a role in maintaining MBC longevity. Using high-resolution imaging, we have provided a description of the earliest events in the Ag activation of MBCs and evidence for acquired cell-intrinsic differences in the initiation of BCR signaling in human naive and MBCs.
authors.affiliation: Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
authors.forename: Angel M
authors.initials: AM
authors.lastname: Davey
authors.forename: Susan K
authors.initials: SK
authors.lastname: Pierce
mesh_terms: D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D016175:B-Lymphocyte Subsets / Q000276:immunology*; D019921:Biotinylation; D005456:Fluorescent Dyes / Q000032:analysis; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D007074:Immunoglobulin G / Q000276:immunology*; D007075:Immunoglobulin M / Q000276:immunology*; D007145:Immunoglobulin kappa-Chains / Q000276:immunology; D007156:Immunologic Memory / Q000276:immunology*; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D008051:Lipid Bilayers; D008213:Lymphocyte Activation / Q000276:immunology*; D008856:Microscopy, Fluorescence / Q000379:methods; D018715:Microscopy, Video; D010766:Phosphorylation; D011494:Protein Kinases / Q000502:physiology; D011499:Protein Processing, Post-Translational; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D011947:Receptors, Antigen, B-Cell / Q000276:immunology*; D017452:Receptors, IgG / Q000276:immunology*; D059010:Single-Cell Analysis; D000072377:Syk Kinase; D059008:Time-Lapse Imaging; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7 / Q000276:immunology
chemical_list: D000888:Antibodies, Anti-Idiotypic; C499173:FCGR2B protein, human; D005456:Fluorescent Dyes; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D007145:Immunoglobulin kappa-Chains; D047908:Intracellular Signaling Peptides and Proteins; D008051:Lipid Bilayers; D011947:Receptors, Antigen, B-Cell; D017452:Receptors, IgG; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7; C048844:anti-IgG; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase