Endoplasmic reticulum aminopeptidases (ERAP) are a class of enzymes responsible for trimming antigenic peptides to facilitate their loading onto major histocompatibility complex (MHC) class I molecules. The ERAP family primarily includes ERAP1 and ERAP2, which are located in the endoplasmic reticulum and participate in the immune surveillance process. These enzymes adjust the length of peptide chains by removing N-terminal residues of antigenic peptides to fit the presentation groove of MHC I molecules. The expression of ERAP genes in different cell types is tissue-specific, and variations in their activity and expression levels are associated with susceptibility to various autoimmune diseases and infectious diseases. Specific genetic variations may affect the enzymatic activity of ERAP, thereby influencing the efficiency of antigen presentation and immune response.