Human lymphocyte antigen molecular typing: how to identify the 1250+ alleles out there.

The human lymphocyte antigen (HLA) typing community was one of the early groups to adopt molecular testing. This action was borne out of the need to identify the many alleles of the highly polymorphic HLA system. Early paradigms used restriction fragment length polymorphism regimes, but the polymerase chain reaction method of amplification quickly replaced that less-than-discriminating choice. Methods currently in use for HLA typing, with commercial kits available, are sequence-specific oligonucleotide probe (both dot blot and the reverse blot dot), sequence-specific primer amplification, restriction fragment length polymorphism of amplified products, double-stranded sequence conformation polymorphism (with and without reference strand), sequence-based typing, and microarray technologies. More than 1250 alleles are recognized by the World Health Organization and meet their criteria for assignment. These alleles can be identified by molecular methods and represent alleles present at class I and class II loci of the HLA complex. On occasion, ambiguous results still persist, even with the best molecular typing methods. Therefore, it is clear to the HLA typing community that a combination of the above methods may be needed to allow true discrimination of the possible alleles an individual carries in their genetic makeup. It is also clear that a typing laboratory may need to resort to nonmolecular serology to understand the significance and impact of the type generated by the HLA molecular typing laboratory.