hla-dqa1 belongs to the hla class ii alpha chain paralogues. this class ii molecule is a heterodimer consisting of an alpha (dqa) and a beta chain (dqb), both anchored in the membrane. it plays a central role in the immune system by presenting peptides derived from extracellular proteins. class ii molecules are expressed in antigen-presenting cells (apc: b lymphocytes, dendritic cells, macrophages).