The HLA system's nomenclature is standardized by the WHO's Nomenclature Committee for Factors of the HLA System. This committee meets regularly during the International Histocompatibility Workshops. At the 15th International Histocompatibility Workshop in Buzios, Brazil, in 2008, new nomenclature rules were established and implemented in April 2010. The HLA system consists of genes located on chromosome 6, encoding over 220 proteins related to the immune system. Initially, antigens were named LA and FOUR, but later replaced by HLA-A, HLA-B, and HLA-C. In the 1970s and 1980s, rules for naming HLA antigens were standardized, using prefixes like HLA followed by locus names and numbers. In 1987, molecular methods introduced the asterisk symbol to denote alleles. In 1990, additional digits were added to describe silent mutations and mutations outside gene regions. In 1991, the "w" suffix was removed from HLA alleles, except for HLA-C. New suffixes like N, L, S, C, A, and Q were introduced to describe allele characteristics. In 2002, due to an increase in alleles, new nomenclature rules were introduced, such as HLA-A*9201 and HLA-B*9501. In 2008, similar changes were made for more than 15 allele groups. The 2010 rules introduced separators in allele names, allowing for more precise classification. Codes P and G were introduced to classify alleles with similar sequences. The new nomenclature is available in the IMGT/HLA database and other resources. The latest version includes 5,302 HLA alleles.The HLA system's nomenclature is standardized by the WHO's Nomenclature Committee for Factors of the HLA System. This committee meets regularly during the International Histocompatibility Workshops. At the 15th International Histocompatibility Workshop in Buzios, Brazil, in 2008, new nomenclature rules were established and implemented in April 2010. The HLA system consists of genes located on chromosome 6, encoding over 220 proteins related to the immune system. Initially, antigens were named LA and FOUR, but later replaced by HLA-A, HLA-B, and HLA-C. In the 1970s and 1980s, rules for naming HLA antigens were standardized, using prefixes like HLA followed by locus names and numbers. In 1987, molecular methods introduced the asterisk symbol to denote alleles. In 1990, additional digits were added to describe silent mutations and mutations outside gene regions. In 1991, the "w" suffix was removed from HLA alleles, except for HLA-C. New suffixes like N, L, S, C, A, and Q were introduced to describe allele characteristics. In 2002, due to an increase in alleles, new nomenclature rules were introduced, such as HLA-A*9201 and HLA-B*9501. In 2008, similar changes were made for more than 15 allele groups. The 2010 rules introduced separators in allele names, allowing for more precise classification. Codes P and G were introduced to classify alleles with similar sequences. The new nomenclature is available in the IMGT/HLA database and other resources. The latest version includes 5,302 HLA alleles.