MHC class I proteins, also known as major histocompatibility complex class I proteins, are a group of cell surface proteins found in vertebrates, including humans. They are involved in the immune response system and play a crucial role in presenting antigens to the immune system for recognition and subsequent destruction.
MHC class I proteins are encoded by a set of genes located in the MHC region. These proteins are expressed on the surface of nearly all nucleated cells and are responsible for presenting intracellularly synthesized antigens to cytotoxic T lymphocytes (CTLs). This process helps the immune system to distinguish between normal, healthy cells and infected or transformed cells that may pose a threat.
The MHC class I protein complex consists of a heavy chain and a smaller protein called β2-microglobulin. The heavy chain is encoded by one of the MHC class I genes and its structure is highly polymorphic, meaning it varies between individuals. This diversity enables the immune system to recognize a wide range of potential antigens.
When a cell becomes infected with a pathogen, viral peptides or other foreign antigens are processed inside the cell and then presented on the cell surface bound to MHC class I proteins. CTLs then scan the surfaces of cells, and if they encounter a foreign antigen presented by MHC class I, they can trigger an immune response, leading to the destruction of the infected or abnormal cells.
Overall, MHC class I proteins are vital components of the immune system, facilitating antigen presentation and helping the body defend against infections, tumors, and other threats.
