Class II glycoproteins are a heterodimer of two alpha chains and two beta chains. All four of these molecules are encoded by HLA genes on chromosome 6. This differs from class I, where only alpha chains are encoded from the HLA genes. The alpha chain alleles are relatively conserved across all class II, with some polymorphisms observed in DQ and DP loci.
The classical HLA Class II antigens are DPB1, DQB1, and DRB1. The DRB beta chain has three other antigen groups: 3, 4, and 5. DRB2 is a pseudogene. DRB1 is linked with DRB3, 4, and 5. Certain DRB1 antigens are associated with the inheritance of certain DRB3, 4, and 5, allowing HLA technologists to predict haplotypes.
- DRB1 is a highly polymorphic locus with thousands of individual alleles. DRB1 has antigens from DRB1*[01:01-DRB1*18:01]. Serologically, this is DR1-DR18.
- DRB3 alleles encode for serological antigen DR52.
- DRB4 alleles encode for serological antigen DR53.
- DRB5 alleles encode for serological antigen DR51.
10. Atropos235. "Schematic representation of MHC class II molecule, consisting of two α-domains and two β-domains. The peptide-binding groove is situated between domains α1and β1." Wikimedia Commons, 18 Mar 2007, https://commons.wikimedia.org/wiki/File:MHC_Class_2.svg
