Co-stimulation

During the activation of lymphocytes, co-stimulation is often crucial to the development of an effective immune response. Co-stimulation is required in addition to the antigen-specific signal from their antigen receptors.

T Cell Co-stimulation

T cells require two signals to become fully activated. A first signal, which is antigen-specific, is provided through the T cell receptor which interacts with peptide-MHC molecules on the membrane of antigen presenting cells (APC). A second signal, the co-stimulatory signal, is antigen nonspecific and is provided by the interaction between co-stimulatory molecules expressed on the membrane of APC and the T cell.

One of the best characterized costimulatory molecules expressed by T cells is CD28, which interacts with CD80 (B7.1) and CD86 (B7.2) on the membrane of APC. Another costimulatory receptor expressed by T cells is ICOS ( Inducible Costimulator), which interacts with ICOS-L.

T cell co-stimulation is necessary for T cell proliferation, differentiation and survival. Activation of T cells without co-stimulation may lead to T cell anergy, T cell deletion or the development of immune tolerance.