The complement inhibitory protein DAF (CD55) suppresses T cell immunity in vivo

J Exp Med. 2005 Feb 21;201(4):567-77. doi: 10.1084/jem.20040863. Epub 2005 Feb 14.


Decay-accelerating factor ([DAF] CD55) is a glycosylphosphatidylinositol-anchored membrane inhibitor of complement with broad clinical relevance. Here, we establish an additional and unexpected role for DAF in the suppression of adaptive immune responses in vivo. In both C57BL/6 and BALB/c mice, deficiency of the Daf1 gene, which encodes the murine homologue of human DAF, significantly enhanced T cell responses to active immunization. This phenotype was characterized by hypersecretion of interferon (IFN)-gamma and interleukin (IL)-2, as well as down-regulation of the inhibitory cytokine IL-10 during antigen restimulation of lymphocytes in vitro. Compared with wild-type mice, Daf1(-/-) mice also displayed markedly exacerbated disease progression and pathology in a T cell-dependent experimental autoimmune encephalomyelitis (EAE) model. However, disabling the complement system in Daf1(-/-) mice normalized T cell secretion of IFN-gamma and IL-2 and attenuated disease severity in the EAE model. These findings establish a critical link between complement and T cell immunity and have implications for the role of DAF and complement in organ transplantation, tumor evasion, and vaccine development.

Publication types

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

MeSH terms

  • Animals
  • CD55 Antigens / genetics
  • CD55 Antigens / immunology*
  • CD55 Antigens / metabolism
  • Cell Proliferation
  • Complement System Proteins / immunology*
  • Disease Models, Animal
  • Encephalomyelitis, Autoimmune, Experimental / immunology
  • Immunization
  • Interferon-gamma / biosynthesis
  • Interleukin-10 / metabolism
  • Interleukin-2 / biosynthesis
  • Lymph Nodes / cytology
  • Lymph Nodes / immunology
  • Male
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Spleen / cytology
  • Spleen / immunology
  • T-Lymphocytes / immunology*


  • CD55 Antigens
  • Interleukin-2
  • Interleukin-10
  • Interferon-gamma
  • Complement System Proteins