We downloaded the functional descriptions of the relevant domains from the interpro database. The members of MHC_I_2 (PF14586) are called retinoic acid-inducible proteins. They are ligands that activate the immune receptor NKG2D. NKG2D is widely expressed on natural killer cells, T cells, and macrophages. MHC_I_C (PF06623) represents the C-terminal region of MHC class I antigen. MHC_I-like_Ag-recog (IPR011161) is an MHC class I antigen recognition sample. Class I MHC glycoproteins are expressed on the surface of all somatic nucleated cells, except neurons. MHC class I receptors present peptide antigens synthesized in the cytoplasm, including self-peptides (offered for self-tolerance) and foreign peptides (such as viral proteins). These antigens are produced by degraded protein fragments transported by the TAP protein (antigenic peptide transporter) to the endoplasmic reticulum, where they can bind to MHC I molecules and then transport them to the cell surface through the Golgi apparatus. MHC class I Receptors display antigens recognized by cytotoxic T cells that can destroy virus-infected or malignant (self-peptide excess) cells. CD8 + T toxic cells and NK cells can recognize class I MHC proteins.