The CD19/CD21 signal transducing complex of human B lymphocytes includes the target of antiproliferative antibody-1 and Leu-13 molecules

J Immunol. 1992 Nov 1;149(9):2841-50.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antigens, CD / physiology*
  • Antigens, CD19
  • Antigens, Differentiation / physiology*
  • Antigens, Differentiation, B-Lymphocyte / physiology*
  • Antigens, Surface / physiology*
  • B-Lymphocytes / immunology*
  • Blotting, Western
  • Calcium / metabolism
  • Cell Adhesion / immunology
  • Cell Line
  • Fluorescent Antibody Technique
  • Humans
  • Lymphocyte Activation / immunology
  • Membrane Proteins*
  • Models, Biological
  • Receptors, Complement 3d / physiology*
  • Signal Transduction / immunology*
  • Tetraspanin 28
  • Transfection


  • Antigens, CD
  • Antigens, CD19
  • Antigens, Differentiation
  • Antigens, Differentiation, B-Lymphocyte
  • Antigens, Surface
  • CD81 protein, human
  • Membrane Proteins
  • Receptors, Complement 3d
  • Tetraspanin 28
  • leu-13 antigen
  • Calcium