title: Enhancement of susceptibility to Fas-mediated apoptosis of TH1 cells by nonmitogenic anti-CD3epsilon F(ab')2.
abstract: BACKGROUND
  Anti-CD3epsilon F(ab')2 are nonmitogenic for naive T cells but can induce apoptosis of antigen-activated T cells in vitro and in vivo. We studied the mechanisms by which nonmitogenic anti-CD3epsilon F(ab')2 antibodies induce T cell death.
  
  
  METHODS
  OVA-responsive T cell lines were generated by immunization in vivo and restimulation in vitro. Fas or Fas ligand (FasL) expression was tested by surface staining with specific mAbs. The apoptotic DNA and cell cycle phase were tested by staining DNA with propidium iodide. Interferon-gamma was measured by ELISA, whereas interleukin (IL)-2 and IL-4 were detected by bioassays.
  
  
  RESULTS
  Restimulation with anti-CD3epsilon F(ab')2 induced apoptosis of antigen-activated wild-type T cells, but not Fas or FasL-defective T cells. Anti-CD3epsilon F(ab')2 induced death of cells expressing high levels of Fas and FasL, and preferentially deleted T helper (Th)1 cells but spared Th2 cells. Soluble anti-CD3epsilon F(ab')2 did not regulate Fas or induce FasL expression, indicating that the ability of anti-CD3epsilon F(ab')2 to induce T cell apoptosis depends on a distinct mechanism. T cells in S/G2 were found relatively resistant to Fas-mediated apoptosis, but anti-CD3epsilon F(ab')2 rendered those T cells exquisitely sensitive to Fas-mediated apoptosis.
  
  
  CONCLUSIONS
  Anti-CD3epsilon F(ab')2 induces apoptosis of cycling CD4+ T cells through activation of the Fas/FasL pathway. Anti-CD3epsilon F(ab')2 does not regulate Fas or FasL expression but induces susceptibility to Fas-mediated apoptosis of cycling T cells. Anti-CD3epsilon F(ab')2 can induce death of polarized Th1 cells, but not Th2 cells, thus potentially skewing the repertoire of antigen-activated T cells toward the Th2 phenotype. These features predict that nonmitogenic anti-CD3epsilon F(ab')2-like antibodies can be useful to prevent or reverse pathogenic immune responses mediated by Th1 cells.
authors.affiliation: Division of Clinical Research, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
authors.forename: X Z
authors.initials: XZ
authors.lastname: Yu
authors.forename: C
authors.initials: C
authors.lastname: Anasetti
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology*; D017209:Apoptosis / Q000502:physiology*; D002453:Cell Cycle; D002460:Cell Line; D053222:Fas Ligand Protein; D007140:Immunoglobulin Fab Fragments / Q000276:immunology*; D008213:Lymphocyte Activation; D008562:Membrane Glycoproteins / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic / Q000235:genetics; D008934:Mitogens / Q000494:pharmacology; D011948:Receptors, Antigen, T-Cell / Q000276:immunology*; D018417:Th1 Cells / Q000502:physiology*; D018418:Th2 Cells / Q000502:physiology; D019014:fas Receptor / Q000502:physiology*
chemical_list: D000906:Antibodies; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D007140:Immunoglobulin Fab Fragments; D008562:Membrane Glycoproteins; D008934:Mitogens; D011948:Receptors, Antigen, T-Cell; D019014:fas Receptor