Representation of T cell activation

Schematic representation of initiation of the immunologic response to an antigen. The antigen binds to a groove in MHC class II molecules on antigen-presenting cells (such as macrophages). This binding allows the antigen to be presented to antigen receptors on autoreactive CD4 inducer or helper T cells, which, in type 1 diabetes mellitus, initiate autoimmune injury to the pancreatic beta cells. In addition, the respective binding of B7 proteins and LFA-3 on antigen-presenting cells to CD28 and CD2 on T cells are important costimulatory pathways that further increase T cell activation. Other molecules can also participate in the immune response, such as the binding of interleukin 2 to its receptor (IL-2R).