CD28/B7 costimulation: a review.
The current model of T cell activation requires two signals. The first signal is specific, requiring T cell receptor recognition and binding to MHC/Antigen presented by an antigen-presenting cell. The second signal is nonspecific, resulting from the binding of B7 ligand on the antigen-presenting cell with its receptor, CD28, on the T cell. If both signals are provided, the T cell will proliferate and secrete cytokines. Recently, it has been shown that CTLA4, another receptor for B7 that is upregulated following T cell after activation, can deliver an inhibitory signal, downregulating T cell proliferation. The B7 family of ligands has two family members, B7-1 and B7-2. They both bind to CD28 and CTLA4, but they differ in their binding affinity, structure, and temporal expression. Considerable research has been done on the CD28/B7 costimulatory pathway. Different ways of manipulating this pathway could provide insights into the mechanism and treatment of opposing pathological states. Blocking the CD28/B7 pathway could result in immunosuppression, with implications for the treatment of autoimmune diseases, organ transplantation, and graft vs. host disease. Activating the CD28/B7 pathway could be useful for including the immune system to recognize and eliminate tumors that evade the immune system. Finally, the CD28/B7 pathway could be involved with maintaining immune tolerance, as recent studies suggest the preferential binding of the B7-CTLA4 pathway results in the down-regulation of the responding T cells. Thus, the B7/CD28/CTLA4 pathway has the ability to both positively and negatively regulate immune responses.
Greenfield
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Department of Adult Oncology, Dana Farber Cancer Institute, Boston, MA 02115, USA.
Nguyen
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Kuchroo
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VK
D000069594:Abatacept; D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000276:immunology; D001327:Autoimmune Diseases; D018122:B7-1 Antigen / Q000276:immunology* / Q000378:metabolism; D018106:CD28 Antigens / Q000276:immunology* / Q000378:metabolism; D060908:CTLA-4 Antigen; D002454:Cell Differentiation; D017635:Clonal Anergy; D006801:Humans; D018796:Immunoconjugates; D008213:Lymphocyte Activation; D009369:Neoplasms / Q000276:immunology; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology*; D014181:Transplantation Immunology
D015703:Antigens, CD; D000943:Antigens, Differentiation; D018122:B7-1 Antigen; D018106:CD28 Antigens; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D018796:Immunoconjugates; D000069594:Abatacept