HLA allele identification and HLA nomenclature
In the clinical settings, the molecular identification of the set of HLA alleles and molecules via low two-digit resolution is performed by serological typing, typically using complement-based or flow cytometric techniques, while the four-digit high-resolution and the allelic resolution involves molecular typing using polymerase chain reaction, DNA sequencing and/or DNA primer hybridisation methods. Molecular typing has been able to identify a large number of HLA alleles and pseudogenes and provides the basis for the current detailed HLA nomenclature, which is very suggested by the World Health Organization HLA Nomenclature Committee. Every HLA allele is first name according to its HLA isotype (ig HLA-A or HLA-DR and so on) followed by an asterisk. Then, a series of digits separated by colons are used to designate different alleles. The first two digits indicate the allele family, corresponding in most occasions on the serological equivalent; the next two or three digits represent the allele number according to its nucleotide sequence, within that allele family, and each allele consisting of a HLA protein differing at least in 1 or 2 amino acids; the next two digits indicate silent synonimous nucleotide differences; and the last two digits indicate differences in the introns or in the 3′ or 5′ non-coding regions.