title: The CD19/CD21 signal transducing complex of human B lymphocytes includes the target of antiproliferative antibody-1 and Leu-13 molecules.
abstract: CD19 is a member of the Ig superfamily expressed on the surface of B lymphocytes that may be involved in the regulation of B cell function. Immunoprecipitation studies with B cell lines solubilized by digitonin have shown CD19 to be part of a multimolecular complex that includes CD21 (CR2) and other unidentified proteins. In this study, two of the CD19-associated proteins were identified as TAPA-1, which is expressed on most cell types, and Leu-13, which is expressed on subsets of lymphoid cells. TAPA-1 and Leu-13 are physically associated in many cell lineages. CD19 and CD21 mAb each specifically coprecipitated proteins of the same size as those precipitated by TAPA-1 and Leu-13 mAb from B cell lines and cDNA-transfected K562 cell lines. Western blot analysis with a TAPA-1 mAb verified the identity of TAPA-1 in CD19 and CD21 immunoprecipitated materials. In addition, when TAPA-1 or Leu-13 were crosslinked and patched on the cell surface, all of the CD19 comigrated with TAPA-1 and some of the CD19 comigrated with Leu-13. Furthermore, mAb binding to CD19, CD21, TAPA-1, and Leu-13 on B cell lines induced similar biologic responses, including the induction of homotypic adhesion, inhibition of proliferation, and an augmentation of the increase in intracellular [Ca2+] induced by suboptimal cross-linking of surface Ig on B cell lines. Together, these data suggest that TAPA-1 and Leu-13 are broadly expressed members of a signal transduction complex in which lineage-specific proteins, such as CD19 and CD21, provide cell-specific functions.
authors.affiliation: Division of Tumor Immunology, Dana-Farber Cancer Institute, Boston, MA 02115-6084.
authors.forename: L E
authors.initials: LE
authors.lastname: Bradbury
authors.forename: G S
authors.initials: GS
authors.lastname: Kansas
authors.forename: S
authors.initials: S
authors.lastname: Levy
authors.forename: R L
authors.initials: RL
authors.lastname: Evans
authors.forename: T F
authors.initials: TF
authors.lastname: Tedder
mesh_terms: D015703:Antigens, CD / Q000502:physiology*; D018941:Antigens, CD19; D000943:Antigens, Differentiation / Q000502:physiology*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000502:physiology*; D000954:Antigens, Surface / Q000502:physiology*; D001402:B-Lymphocytes / Q000276:immunology*; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002448:Cell Adhesion / Q000276:immunology; D002460:Cell Line; D005455:Fluorescent Antibody Technique; D006801:Humans; D008213:Lymphocyte Activation / Q000276:immunology; D008565:Membrane Proteins; D008954:Models, Biological; D017464:Receptors, Complement 3d / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology*; D060225:Tetraspanin 28; D014162:Transfection
chemical_list: D015703:Antigens, CD; D018941:Antigens, CD19; D000943:Antigens, Differentiation; D000944:Antigens, Differentiation, B-Lymphocyte; D000954:Antigens, Surface; C554798:CD81 protein, human; D008565:Membrane Proteins; D017464:Receptors, Complement 3d; D060225:Tetraspanin 28; C062010:leu-13 antigen; D002118:Calcium