title: Costimulatory pathways as a basic mechanisms of activating a tolerance signal in T cells.
abstract: Immune tolerance is an active response leading to the T cell unresponsiveness in the presence of the graft, which may develop through a couple of mechanisms including costimulation blockade. The CD28/B7 and CD40L/CD40 costimulatory pathways have been described as the critical for T cell activation. When activated T cell upregulate CTLA4, which importance as a negative regulatory costimulatory molecule is highlighted by the recent evidence suggesting that CTLA4 may function as a master switch for peripheral T cell tolerance. The effects of CTLA4 engagement are directed at the inhibition of CD28 signaling. Modulation of proximal TCR signals and down-stream effector pathways of T cell activation result in altered T cell differentiation and downregulation of immune responses. CTLA4 may regulate signal transduction in a rare subset of CD4+CD25 + T cells which leads to differentiation into regulatory cells. CD40L/CD40 interaction provides a bi-directional signal for T and B cell activation. A possible mechanisms of tolerance induction by CD40L/CD40 blockade involve reduction in expression of B7 molecules, effects on bcl-xL gene and APC function modification. The role of the new discovered pathways: ICOS/B7RP-I and PD-I/PD-LI in regulation of T cell response in transplantation is becoming apparent.
authors.affiliation: Department of Nephrology and Transplantation Medicine, Medical University of Wrocław, Poland. klinef@am.centrum.pl
authors.forename: Maria
authors.initials: M
authors.lastname: Magott-Procelewska
mesh_terms: D000818:Animals; D000945:Antigens, Differentiation, T-Lymphocyte / Q000378:metabolism; D001402:B-Lymphocytes / Q000276:immunology; D018122:B7-1 Antigen / Q000378:metabolism*; D018106:CD28 Antigens / Q000378:metabolism*; D019013:CD40 Antigens / Q000378:metabolism*; D023201:CD40 Ligand / Q000378:metabolism*; D006801:Humans; D060889:Inducible T-Cell Co-Stimulator Protein; D016377:Organ Transplantation; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D023001:Transplantation Tolerance
chemical_list: D000945:Antigens, Differentiation, T-Lymphocyte; D018122:B7-1 Antigen; D018106:CD28 Antigens; D019013:CD40 Antigens; C556692:ICOS protein, human; D060889:Inducible T-Cell Co-Stimulator Protein; D023201:CD40 Ligand