Polymorphisms of human immunoglobulins: Gm, Am, Em and Km allotypes

A brief review of the polymorphisms of human immunoglobulins (Ig) is presented here as the introductory paper of this special issue on Ig allotypes. The different allelic forms of the Ig genes for the heavy chains of IgG1, IgG2, IgG3, IgA2 and IgE and for the kappa light chains, which give rise to the G1m, G2m, G3m, A2m, Em and Km allotypes, respectively, are discussed. Until now, 24 allotypes have been described and confirmed by other investigators: 4 G1m, 1 G2m, 13 G3m, 2 A2m, 1 Em and 3 Km allotypes. The alleles of the heavy chain genes are inherited in haplotypes because these genes are located close to each other on chromosome 14. The variations in haplotype frequencies in different populations and the occurrence of isoallotypes in IgG and IgA subclasses are discussed. Applications of Ig allotyping and new developments in this field are mentioned with reference to the other papers in this issue.