title: The CR2/CD19 complex on human B cells contains the src-family kinase Lyn.
abstract: The complement receptor 2 (CR2 or CD21) can be found in non-covalent association with the B lymphocyte specific CD19 complex at the surface of mature human B cells. Upon ligation of the B cell antigen receptor complex (BCR), members of the CR2-CD19 complex may associate with membrane immunoglobulin (mlg). Moreover, CD19 and CD21 ligands, either murine mAb, C3d fragments or Epstein-Barr virus, are known to have profound effects on B cell activation. We here show that CD19 is tightly linked to the non-receptor src kinase Lyn and that the CD19 glycoprotein itself serves as a substrate for a yet undefined serine/threonine kinase present within the complex. In the process of antigen recognition, mlg and the CR2-CD19 complex may bind different sites of a complement-opsonized antigenic particle. We hypothesize that in this process, approximation to the BCR allows CD19-associated Lyn kinase to phosphorylate potential substrates within the antigen-receptor complex, thereby effecting its coupling to the intracellular compartment.
authors.affiliation: Department of Clinical Viro-Immunology, Central Laboratory of The Netherlands Red Cross Blood Transfusion Service, Amsterdam.
authors.forename: C J
authors.initials: CJ
authors.lastname: van Noesel
authors.forename: A C
authors.initials: AC
authors.lastname: Lankester
authors.forename: G M
authors.initials: GM
authors.lastname: van Schijndel
authors.forename: R A
authors.initials: RA
authors.lastname: van Lier
mesh_terms: D015703:Antigens, CD / Q000032:analysis*; D018941:Antigens, CD19; D000944:Antigens, Differentiation, B-Lymphocyte / Q000032:analysis*; D001402:B-Lymphocytes / Q000201:enzymology / Q000276:immunology*; D015704:CD4 Antigens / Q000032:analysis; D006801:Humans; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000032:analysis*; D017464:Receptors, Complement 3d / Q000032:analysis; D019061:src-Family Kinases
chemical_list: D015703:Antigens, CD; D018941:Antigens, CD19; D000944:Antigens, Differentiation, B-Lymphocyte; D015704:CD4 Antigens; D017464:Receptors, Complement 3d; D011505:Protein-Tyrosine Kinases; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases