HLA-DPA1 Protein, Human (His)

The HLA-DPA1 Protein plays a pivotal role in the immune system by binding peptides derived from antigens within the endocytic route of antigen-presenting cells (APCs) and presenting them on the cell surface for recognition by CD4 T-cells. The peptide binding cleft of HLA-DPA1 accommodates peptides ranging from 10 to 30 residues, predominantly generated through the degradation of proteins accessing the endocytic route. This exogenous antigen presentation pathway involves lysosomal proteases and other hydrolases processing antigens taken up by APCs. Notably, cells of the gastrointestinal tract, including epithelial cells, express MHC class II molecules and CD74, acting as unconventional APCs. The assembly of a functional MHC class II molecule involves the association of three MHC class II molecules with a CD74 trimer in the endoplasmic reticulum (ER), forming a heterononamer. Upon entering the endosomal/lysosomal system, CD74 undergoes sequential degradation, leaving a fragment known as CLIP on each MHC class II molecule. HLA-DM facilitates CLIP removal, stabilizing MHC class II until high-affinity antigenic peptides bind. HLA-DO regulates the interaction between HLA-DM and MHC class II in B-cells, and lysosomal acidification influences efficient peptide loading. The MHC class II molecule, bound to a peptide, is then transported to the cell membrane surface for immune recognition.