Class I MHC
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MHC class I molecules are cell surface proteins found on most cells of the body. These proteins have a distinctive structure first elucidated in 1987 by Dr. Pamela J. Bjorkman and colleagues. MHC molecules typically interact with the cell surface receptor of a type of lymphocytes known as killer T cells. The receptor on the killer T cell binds to the MHC molecule and informs the killer T cell on whether that cell is normal or not. The interesting part of the story is how the T cell can distinguish the MHC class I protein on a normal cell from that on an abnormal one. The key concept here is to appreciate that the MHC molecule has within its structure a groove. Into this groove is bound a small piece of protein derived from within the cell, that was placed there during the synthesis of the MHC molecule. If this peptide of 8 or 9 amino acids happens to be a foreign peptide, such as one produced by a viral gene, or a cancer gene, the T cell will become activated, and attack the infected or cancerous cell. Of course there many more details involved in this process. Of primary interest to medicine and the average person is the fact that when an organ is transplanted between non-identical people, it is the recipient's T cells reacting against the donor organ MHC proteins that causes much of organ rejection.