The Nomenclature Committee for Factors of the HLA System of the World Health Organization (WHO) standardizes the nomenclature of the HLA system, which is highly polymorphic and located on chromosome 6. The committee meets regularly during the International Histocompatibility Workshops (IHWS). New rules were established at the 15th IHWS in Búzios, Brazil, in September 2008, and implemented in April 2010. These changes include expanding allele names with separators to divide groups, specificities, silent mutations, and intron variations, ensuring all alleles are named with at least four digits. The "w" suffix for alleles of the C locus was dropped to distinguish them from complement system factors and KIR ligands. Additionally, codes P and G were introduced to address ambiguity in alleles with different nucleotide sequences but the same protein coding. The official sequences and alleles are available in the IMGT/HLA database and journals such as Tissue Antigens, Human Immunology, and International Journal of Immunogenetics.The Nomenclature Committee for Factors of the HLA System of the World Health Organization (WHO) standardizes the nomenclature of the HLA system, which is highly polymorphic and located on chromosome 6. The committee meets regularly during the International Histocompatibility Workshops (IHWS). New rules were established at the 15th IHWS in Búzios, Brazil, in September 2008, and implemented in April 2010. These changes include expanding allele names with separators to divide groups, specificities, silent mutations, and intron variations, ensuring all alleles are named with at least four digits. The "w" suffix for alleles of the C locus was dropped to distinguish them from complement system factors and KIR ligands. Additionally, codes P and G were introduced to address ambiguity in alleles with different nucleotide sequences but the same protein coding. The official sequences and alleles are available in the IMGT/HLA database and journals such as Tissue Antigens, Human Immunology, and International Journal of Immunogenetics.