Immunological Barriers to Stem Cell Therapy in the Central Nervous System

Figure 1

MHC I antigen presentation pathway. In this diagram the peptides derive from viruses that are taken into the cell by endocytosis. However, this could be any protein. The virus escapes the endosomes into the cytoplasm where it is transcribed and translated (ribosomes at the top). Some proteins also escape later into the cytoplasm. As these proteins become dysfunctional, they are labeled with ubiquitin (black rectangle) and transported to the proteosome in which the proteins are degraded into small peptides. These peptides translocated into the endoplasmic reticulum (ER) by the transporter associated with antigen processing (TAP). They are cleaved further in the ER by the ER associated peptidase (ERAP). MHC I is synthesized in the ER and dimerizes with beta-2-microglobulin (𝛽2m). MHC I binds to small peptides in the ER and the MHC I-peptide complexes are transported to the cell surface in exocytic vesicles.