Major Histocompatibility Complex Class II DO Alpha （HLA-DOA） is a significant modulator in the HLA class II restricted antigen presentation pathway by interaction with the HLA-DM molecule in B-cells. HLA-DOA forms a heterodimer along with HLA-DOB. The heterodimer is located in lysosomes in B cells and regulates HLA-DM-mediated peptide loading on MHC class II molecules. HLA-DOA exhibits very little sequence variation， particularly at the protein level.
