Immunological Barriers to Stem Cell Therapy in the Central Nervous System

Figure 4

Points of action of immunosuppressive drugs. Various types of immunosuppressive drugs are shown in red and their targets are indicated by red arrows. In this example, we are showing the interaction of T cell receptor (TCR) proteins with MHC II-peptide complexes on the surface of antigen presenting cells (APC). TCRs also bind to MHC I-peptides on CD8⁺ T cells. The TCR signal is enhanced by the binding of B7 on the surface of APCs to CD28 on T cells. The binding of IL-2 to its receptor (IL-2R) on T cells results in proliferation and differentiation of the T cells into effector and memory cells. Humans express a second form of IL-2R that is soluble in serum, because it is missing the transmembrane domain of Il-2R. Soluble IL-2R binds and reduces the serum levels of IL-2.