Human Gm, Km, and Am Allotypes: WHO/IMGT Nomenclature and IMGT Unique Numbering for Immunoinformatics and Therapeutical Antibodies

Human immunoglobulin allotypes are allelic antigenic determinants (or “markers”) determined serologically, classically by hemagglutination inhibition, on the human immunoglobulin (IG) or antibody heavy and light chains. The allotypes have been identified on the gamma1, gamma2, gamma3, and alpha2 heavy chains (designated as G1m, G2m, G3m, and A2m allotypes, respectively) and on the kappa light chain (Km allotypes). Gm and Am allotypes have been one of the most powerful tools in population genetics, as they are inherited in fixed combinations, or Gm–Am haplotypes, owing to the linkage of the human IGHC genes in the IGH locus on chromosome 14. They have been very instrumental in molecular characterization of the human IGHC genes (gene polymorphisms or alleles, and IG heavy-chain structure in domains) and of the IGH locus (IGHC gene order, gene conversion, and copy number variation (CNV)). They represent a major system for understanding immunogenicity of the polymorphic IG chains in relation to amino acid and conformational changes. The WHO/IMGT allotype nomenclature and the IMGT unique numbering for constant (C) domain bridge Gm–Am and Km alleles to IGHC and IGKC gene alleles and structures and, by definition, to IG chain immunogenicity, opening the way for immunoinformatics of personalized therapeutic antibodies and engineered variants.