title: [Regulation of T-cell activation by CD28 and CTLA-4].
abstract: T CELL RESPONSE: T lymphocytes play a key role in the coordination of the immune response. T helper cells contribute primarily by means of cytokine release, whereas cytotoxic T cells eliminate cells bearing antigens recognized as foreign. Through its T cell receptor each T cell can recognize a specific peptide antigen, which is presented in the context of the major histocompatibility complex (MHC) to T helper cells by specialized antigen-presenting cells or to cytotoxic T cells by nearly all body cells. Upon contact with its specific antigen, the T cell receptor transduces an activation signal into the T cell, leading to proliferation, cytokine production, or efficient cytotoxicity.
  However, a second costimulatory signal is necessary to achieve complete activation. This can be provided by the accessory T cell molecule CD28 upon binding to its respective ligands B7-1 (CD80) or B7-2 (CD86). The same ligands bind to CTLA-4 (CD152), a receptor expressed at the surface of T cells previously activated for 2 to 3 days and capable of downregulating activation. IMMUNOSUPPRESSION BY CTLA-4Ig: A genetically engineered soluble fusion protein containing the extracellular domain of CTLA-4 and the Fc portion of an immunoglobulin heavy chain (CTLA-4Ig) prevents the interaction of CD28 and CTLA-4 with their B7 ligands, the subsequent activation of T cells and thereby eliminates or reduces unfavorable immune system activation in transplant rejection or autoimmunity.
  
  
  CONCLUSIONS
  The importance of the regulatory system comprising CD28, CTLA-4 and the B7 molecules and its modulation by CTLA-4Ig has been demonstrated in a substantial number of animal models in recent years and holds promise as a novel approach for therapeutic immunomodulation in humans.
authors.affiliation: Medizinische Klinik III und Institut für Klinische Immunologie, Friedrich-Alexander-Universität Erlangen-Nürnberg.
authors.forename: T
authors.initials: T
authors.lastname: Nagel
authors.forename: J R
authors.initials: JR
authors.lastname: Kalden
authors.forename: B
authors.initials: B
authors.lastname: Manger
mesh_terms: D000069594:Abatacept; D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000502:physiology*; D018106:CD28 Antigens / Q000502:physiology*; D060908:CTLA-4 Antigen; D006801:Humans; D018796:Immunoconjugates; D008213:Lymphocyte Activation / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D018106:CD28 Antigens; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D018796:Immunoconjugates; D000069594:Abatacept
vernacular_title: Regulation der T-Zell-Aktivierung über CD28 und CTLA-4.