Clinical Pathology: General Principles, Immunology & Histocompatibility

• Human leukocyte antigen (HLA) nomenclature began by assigning each locus consecutive numbers corresponding to new anti-HLA antibodies discovered (HLA-A1, -A2, etc).

• It was realized early on that some anti-HLA antibodies recognized multiple HLAs, hence the need to “split” what was formerly thought to be a single antigen into newly discovered subtypes, that is, B16B38, B39; B17B57, B58.

• With the advent of genetics, HLA loci were discovered to be much more polymorphic than could ever be classified by serology. For example, at the genetic level, HLA-B57 appeared to be a collection of alleles B*57:01, B*57:02, etc.

• In this nomenclature convention (i.e., B*57:01), the first two numbers represent the serologically defined antigen and the second two represent the allelic subtype.

• Finally, in 2011 a new nomenclature was introduced to address the problem that arises at loci that have more than 99 genetically defined alleles – that is, HLA-B*5799 would be the last allele in which the genetic resolution can be described by two digits. The newest nomenclature looks like HLA-B*57:01:02, and the last two digits define alleles of B*57:01 with silent mutations.

• Patients with long allograft survival times may have typing results in their charts and medical records conforming to outdated nomenclatures.

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