A role for CD9 molecules in T cell activation

J Exp Med. 1996 Aug 1;184(2):753-8. doi: 10.1084/jem.184.2.753.


Costimulation mediated by the CD28 molecule plays an important role in optimal activation of T cells. However, CD28-deficient mice can mount effective T cell-dependent immune responses, suggesting the existence of other costimulatory systems. In a search for other costimulatory molecules on T cells, we have developed a monoclonal antibody (mAb) that can costimulate T cells in the absence of antigen-presenting cells (APC). The molecule recognized by this mAb, 9D3, was found to be expressed on almost all mature T cells and to be a protein of approximately 24 kD molecular mass. By expression cloning, this molecule was identified as CD9, 9D3 (anti-CD9) synergized with suboptimal doses of anti-CD3 mAb in inducing proliferation by virgin T cells. Costimulation was induced by independent ligation of CD3 and CD9, suggesting that colocalization of these two molecules is not required for T cell activation. The costimulation by anti-CD9 was as potent as that by anti-CD28. Moreover, anti-CD9 costimulated in a CD28-independent way because anti-CD9 equally costimulated T cells from the CD28-deficient as well as wild-type mice. Thus, these results indicate that CD9 serves as a molecule on T cells that can deliver a potent CD28-independent costimulatory signal.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal / immunology
  • Antigens, CD / physiology*
  • CD28 Antigens / physiology
  • CD3 Complex / immunology
  • Cloning, Molecular
  • DNA, Complementary / genetics
  • Lymphocyte Activation*
  • Membrane Glycoproteins*
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred C57BL
  • T-Lymphocytes / immunology*
  • Tetraspanin 29


  • Antibodies, Monoclonal
  • Antigens, CD
  • CD28 Antigens
  • CD3 Complex
  • Cd9 protein, mouse
  • DNA, Complementary
  • Membrane Glycoproteins
  • Tetraspanin 29