protein MHC class II histocompatibility antigen alpha chain Category=family. Note: There are three major and two minor class II MHC (major histocompatability complex) alpha chain genes in human. Designations for the MHC complex loci are species specific: HLA (human leukocyte antigen) in human, H-2 in mouse. MHC class II loci are characterized by large numbers of allelic variants. In contrast to MHC Class I alpha chain genes, orthologies can be seen between some human and mouse genes. MHC class II alpha chains form heterodimers with MHLC class II beta chains. MHCcIIalpha A protein with core architecture consisting of a signal sequence, a Class II histocompatibility antigen, alpha domain (Pfam:PF00993) and an Immunoglobulin C1-set domain (Pfam:PF07654); these form the extracellular domain and are followed by a single-pass transmembrane region and a small cytoplasmic region. PR:000001820 protein