Serum Gm allotype development during childhood

Gm allotypes are genetic variants of the immunoglobulin heavy G chains (IGH G) of IgG molecules, coded from chromosome 14q32, characterized by differen ces in amino acid epitopes of the constant heavy G chains and inherited in the Mendelian manner. Gm allotypes have influence on IgG subclass levels, a nd serum Gm allotype levels have been given for different Gm genotypes in a dults. Four hundred and thirty healthy children, aged 1-15 years, were exam ined for serum Gm allotypes and TgG subclasses from the six most common Gm genotypes and different age groups were measured using competitive enzyme-l inked immunosorbant assay and radial immunodiffusion methods. Quantities (i n g/l) of G1m(a) and G1m(f) of IgG I, G2m(n) and G2m(n) of IgG2 and G3m(g), and G3m(b) of IgG3 an given. Different maturation rates of the alternative Gm allotypes within IgG1, IgG2 and IgG3 were shown. G2m(n) development was strikingly retarded compared with G2m(-n) from the gamma 2 locus. This was found comparing IgG2 levels from homozygous G2m(-n-n) and G2m(nn) individu als, but was also seen in heterozygous G2m(n-n) genotypes. From the gamma 1 locus Glm(f) levels dominated significantly, but inconstantly, over G1m(a) levels in heterozygous G1m(af) individuals. Tn homozygous G1m genotypes, G 1m(aa) compared with G1m(ff) of the same age, one or the other dominated, s ometimes significantly. Serum levels of G3m(b) from the gamma 3 locus of ho mozygous G3m(bb) individuals were increased significantly compared with G3m (g) levels of homozygous G3m(gg) individuals, in ages over 3 years. However , in heterozygous G3m(gb) individuals G3m(b) dominance was not evident. The re is a relatively rapid development of G1m(f) molecules and a retarded dev elopment of G2m(n) in the Gm(f;n;b) haplotype. In comparison, G1m(a) is ret arded and G2m(-n) is enhanced in the Gm(a;-n;g) haplotype. The retarded ser um G2m(n) development is comparable with serum IgA development during child hood. Different maturation rates of Gm allotypes within the same IgG subcla ss provide further explanation for the variation of the antibody response d uring childhood. Quantitative Gm allotype determinations give information o f the activity from IGHG genes. The genetic variation constitutes an additi onal basis for evaluation of IgG antibodies in different diseases in childh ood.