Old game, new players: Linking classical theories to new trends in transplant immunology

Figure 4 Examples of co-stimulatory receptors in immune synapse interactions. T cell activation depends not only on the antigen-specific signals provided by MHC-TCR signaling but also on a complex balance of co-stimulatory signals that may enhance or inhibit activation. These receptors are mainly classified into the immunoglobulin superfamily (IgSF) or the tumor necrosis factor receptor superfamily (TNFRSF) and may provide positive (black arrows) or negative signals (red arrows), or even apoptotic signals (red dashed arrow), which in turn decide cell fate. MHC: Major histocompatibility complex; TCR: T cell receptor.