The Human Leukocyte Antigen System

Human leukocyte antigens are polymorphic cell-surface molecules that are intimately involved in the regulation of the immune response. The antigens are encoded by a series of closely linked genes known as the major histocompatibility complex (MHC), which is located on the short arm of chromosome 6 (BIO). The complex extends over approximately 4000 kilobases or 4 x 10 nucleotides and contains three distinct subregions known as class I, class II, and class III (T19) (see Fig. 1). 

The nomenclature of the HLA system is determined by the World Health Organization (WHO) Nomenclature Committee and reflects both the serological and the nucleotide levels of classification. The 1991 report of the Nomenclature Committee listed 27 HLA-A specificities, 59 HLA-B specificities, and 10 HLA-C specificities as shown in Table 1 (B17). These are the specificities that are detectable at the serological level. Contributing to some of these individual specificities, however, can be a large number of different alleles. At least 10 different alleles code for the specificity HLA-A2, for example, and 7 code for HLA-B27. To accommodate this complexity, the Nomenclature Committee has 

Specificities with numbers in parentheses represent broad specificities that include two or more subgroups. For example, the broad specificity HLA-A19 includes the subgroups A29, A30, A31, A32, A33, and A74. The number in parentheses indicates the broad specificity associated with that subgroup. Inclusion of the parenthesized number is optional when referring to a subgroup. Thus, it is not necessary to refer to A33(19) the short form A33 is acceptable. Use of the prefix HLA for a specificity name is optional HLA-B46 and B46 are equally acceptable to refer to that specificity. 

List of HLA-A, -B, and -C Alleles for Which Unique Nucleotide Sequences Have Been Determined 

HLA-A alleles HLA-A specificity HLA-B alleles HLA-B specificity HLA-C alleles HLA-C specificity 

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