title: Analysis of the CD40 and CD28 pathways on alloimmune responses by CD4+ T cells in vivo.
abstract: BACKGROUND
  Blockade of the CD40 and CD28 pathways is a powerful strategy to inhibit CD4-mediated alloimmune responses. In this study, we examine the relative roles of the CD40 and CD28 pathways on CD4-mediated allograft rejection responses, and further characterize the role of these pathways on CD4+ T-cell activation, priming for cytokine production, and cell proliferation in response to alloantigen in vivo.
  
  
  METHODS
  BALB/c skin allografts were transplanted onto C57BL/6 Rag 1-/- recipients reconstituted with CD4 cells from CD28-/- or CD40L-/- donors. The popliteal lymph node assay was used to study the role of these pathways on CD4-cell activation and priming in vivo. To investigate the role of CD40 and CD28 blockade on CD4-cell proliferation, the fluorescein dye carboxyfluorescein diacetate succinimidyl ester was used. We performed heterotopic cardiac transplantation using CD40-/- mice to evaluate the role of CD40 on donor versus recipient cells in CD4-mediated rejection.
  
  
  RESULTS
  B6 Rag 1-/- recipients reconstituted with CD28-/- CD4+ T cells acutely rejected allografts (median survival time 15 days), whereas recipients reconstituted with CD40L-/- CD4+ T cells had significantly prolonged survival of BALB/c skin grafts (MST 71 days). CD40L blockade was equivalent to or inferior to CD28 blockade in inhibition of in vivo CD4-cell activation, priming for cytokine production, and proliferation responses to alloantigen. BALB/c recipients depleted of CD8 cells promptly rejected donor B6 CD40-/- cardiac allografts, whereas B6 CD40-/- recipients depleted of CD8 cells had significantly prolonged survival of BALB/c wild-type cardiac allografts.
  
  
  CONCLUSIONS
  The CD40/CD40L pathway, but not the CD28/B7 pathway, is critical for CD4-mediated rejection responses, however, the responsible mechanisms remain unclear.
authors.affiliation: The Carlos and Marguerite Mason Transplantation Biology Research Center, Department of Surgery, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
authors.forename: A W
authors.initials: AW
authors.lastname: Bingaman
authors.forename: J
authors.initials: J
authors.lastname: Ha
authors.forename: M M
authors.initials: MM
authors.lastname: Durham
authors.forename: S Y
authors.initials: SY
authors.lastname: Waitze
authors.forename: C
authors.initials: C
authors.lastname: Tucker-Burden
authors.forename: S R
authors.initials: SR
authors.lastname: Cowan
authors.forename: T C
authors.initials: TC
authors.lastname: Pearson
authors.forename: C P
authors.initials: CP
authors.lastname: Larsen
mesh_terms: D000818:Animals; D018106:CD28 Antigens / Q000502:physiology*; D015704:CD4 Antigens / Q000502:physiology; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000473:pathology / Q000502:physiology*; D019013:CD40 Antigens / Q000502:physiology*; D023201:CD40 Ligand / Q000235:genetics; D002455:Cell Division / Q000502:physiology; D016207:Cytokines / Q000096:biosynthesis; D006084:Graft Rejection / Q000503:physiopathology; D016027:Heart Transplantation; D007109:Immunity / Q000502:physiology*; D007519:Isoantigens / Q000276:immunology*; D008213:Lymphocyte Activation; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout / Q000235:genetics; D009206:Myocardium / Q000473:pathology; D016038:Skin Transplantation / Q000276:immunology / Q000502:physiology; D014184:Transplantation, Homologous
chemical_list: D018106:CD28 Antigens; D015704:CD4 Antigens; D019013:CD40 Antigens; D016207:Cytokines; D007519:Isoantigens; D023201:CD40 Ligand