The activation of T-lymphocytes plays a central role in inflammatory reactions and in graft rejections. It requires that, in addition to the antigen recognition signal via the T cell receptor (TZR), costimulatory signals are triggered via accessory receptors such as CD2 or CD28. Antigen recognition without costimulatory signals is not an indifferent event for T cells. Rather, it leads to antigen-specific unreactivity(anergy).
This is one of the immunological mechanisms that lead to T-lymphocytes not being directed against the body's own structures, i.e. not being autoreactive.
Costimulatory signals are therefore important target structures for immunomodulation strategies. Costimulatory signals are triggered in vivo by binding accessory receptors to their ligands(CD80, CD86 and CD58) on antigen-presenting cells (APZ).