HLA-D and DR in different populations

The HLA-D-segregant series of lymphocyte activating determinants (Lads) was originally described by using homozygous cells as reagents in mixed lymphocyte cultures (MLC). Later, the serological definition of the HLA-DR antigens was established by using HLA-D homozygous cells (HTCs) as reference cells. It appeared in Caucasoid panels that the two techniques were detecting the same antigenic determinants. Further serological, biochemical, and DNA studies have now revealed the complexity of the HLA-D region, but the relationship between D and DR remains unresolved.