title: CD19 controls Toll-like receptor 9 responses in human B cells.
abstract: BACKGROUND
  CD19 is a B cell-specific molecule that serves as a major costimulatory molecule for amplifying B-cell receptor (BCR) responses. Biallelic CD19 gene mutations cause common variable immunodeficiency in human subjects. BCR- and Toll-like receptor (TLR) 9-induced B-cell responses are impaired in most patients with common variable immunodeficiency.
  
  
  OBJECTIVE
  We sought to analyze whether CD19 is required for TLR9 function in human B cells.
  
  
  METHODS
  Expression of surface activation markers was assessed after anti-IgM or CpG stimulation by using flow cytometry on B cells from patients with 1 or 2 defective CD19 alleles, which decrease or abrogate CD19 expression, respectively. The phosphorylation or interaction of signaling molecules was analyzed by using phospho flow cytometry, immunoblotting, or co-immunoprecipitation in CD19-deficient or control B cells and in a B-cell line in which CD19 has been knocked down with lentivirus-transduced short hairpin RNA.
  
  
  RESULTS
  B cells from subjects with 1 or 2 defective CD19 alleles showed defective upregulation in vitro of CD86, transmembrane activator and CAML interactor (TACI), and CD23 activation markers after TLR9 stimulation. TLR9 ligands normally induce phosphorylation of CD19 through myeloid differentiation primary response gene-88 (MYD88)/proline-rich tyrosine kinase 2 (PYK2)/LYN complexes, which allows recruitment of phosphoinositide 3-kinase (PI3K) and phosphorylation of Bruton tyrosine kinase (BTK) and AKT in human B cells with a different kinetic than that of BCRs. In addition, inhibition of PI3K, AKT, or BTK, as well as BTK deficiency, also resulted in TLR9 activation defects in B cells similar to those in patients with CD19 deficiency.
  
  
  CONCLUSIONS
  CD19 is required for TLR9-induced B-cell activation. Hence CD19/PI3K/AKT/BTK is an essential axis integrating BCRs and TLR9 signaling in human B cells.
authors.affiliation: Department of Immunobiology, Yale University School of Medicine, New Haven, Conn.
authors.forename: Henner
authors.initials: H
authors.lastname: Morbach
authors.affiliation: Department of Immunobiology, Yale University School of Medicine, New Haven, Conn.
authors.forename: Jean-Nicolas
authors.initials: JN
authors.lastname: Schickel
authors.affiliation: Department of Medicine, Mount Sinai Medical Center, New York, NY.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Cunningham-Rundles
authors.affiliation: Department of Pediatrics, University of Tennessee College of Medicine, Memphis, Tenn.
authors.forename: Mary Ellen
authors.initials: ME
authors.lastname: Conley
authors.affiliation: Department of Immunology and Allergy, Meram Medical Faculty, Selcuk University, Konya, Turkey.
authors.forename: Ismail
authors.initials: I
authors.lastname: Reisli
authors.affiliation: Group of Primary Immunodeficiencies, University of Antioquia, Medellin, Colombia.
authors.forename: Jose Luis
authors.initials: JL
authors.lastname: Franco
authors.affiliation: Department of Immunobiology, Yale University School of Medicine, New Haven, Conn. Electronic address: eric.meffre@yale.edu.
authors.forename: Eric
authors.initials: E
authors.lastname: Meffre
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D018941:Antigens, CD19 / Q000235:genetics* / Q000378:metabolism*; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism*; D016022:Case-Control Studies; D051418:Focal Adhesion Kinase 2 / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D016130:Immunophenotyping; D008213:Lymphocyte Activation / Q000235:genetics / Q000276:immunology; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism; D051217:Toll-Like Receptor 9 / Q000819:agonists / Q000378:metabolism*
chemical_list: D000077329:Agammaglobulinaemia Tyrosine Kinase; D018941:Antigens, CD19; D051418:Focal Adhesion Kinase 2; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011505:Protein-Tyrosine Kinases; D051057:Proto-Oncogene Proteins c-akt; D011947:Receptors, Antigen, B-Cell; D051217:Toll-Like Receptor 9; C000625949:BTK protein, human
keywords: AKT; B cells; Bruton tyrosine kinase; CD19; Toll-like receptor 9; common variable immunodeficiency; phosphoinositide 3-kinase