| مستخلص: |
Most genetic studies of bronchial asthma deal with IgE responsiveness. The manner by which allergens trigger IgE production and activate mast cells suggests that several genetic loci may be involved. Several reports of candidate genes include chromosome 6 and HLA antigens, chromosome 14q11 and the α chain of the T cell receptor, chromosome 11q32 and the β chain of the high-affinity IgE receptor and chromosome 5 and the gene cluster for IL-4, respectively. In addition, the immunoglobulin heavy chain G (IGHG) genes on chromosome 14q32 have been associated with both atopic and non atopic bronchial asthma in children. In order to further investigate the role of IGHG genes in asthmatic children, the phenotypes of patients with homozygous but alternative IGHG genes were investigated. IGHG gene expression of patients with childhood asthma was determined by serum Gm allotypes with a quantitative competitive indirect ELISA method. The groups consisted of 24 children with the homozygous G3m(b/b)-G1m(f/f )-G2m(n/n) and 16 with the alternative G3m(g/g)-G1m(a/a)-G2m(–n/–n) genes. The two different genotypes were investigated for serum IgE (PRIST), serum IgG subclass levels (radial immunodiffusion), Gm allotype levels (competitive ELISA), IgA and IgM levels (radial immunodiffusion), peripheral blood eosinophils, specific IgE antibodies (skin prick test, SPT, or radioallergosorbent test, RAST), number of peripheral blood CD lymphocyte markers (flow cytometry) and serum IL-4 and IFN-γ levels (ELISA). Comparison of the two genotypes in children with bronchial asthma revealed significantly increased IgE (p < 0.001), increased specific IgE (p < 0.001), as investigated by SPT or RAST (n = 10 allergens tested), increased number of peripheral blood eosinophils (p < 0.01), increased serum IgG1(f/f )(p < 0.001), IgG2(n/n)(p < 0.001) and IgG3(b/b)(p < 0.01) levels, and decreased CD8 given in percent of the total number of peripheral lymphocytes, (p < 0.02) in the G3m(b/b)-G1m(f/f )-G2m(n/n) genotype. The asthmatic children with the G3m(g/g)-G1m(a/a)-G2m(–n/–n) genes instead showed low IgE levels, practically no specific IgE antibodies, a lower number of peripheral blood eosinophils, lower IgG1(a/a), IgG2(–n/–n) and IgG3(g/g) serum levels and higher CD8 lymphocyte numbers. The results show that the IGHG3(b/b)-IGHG1(f/f )-IGHG2(n/n) genes are in linkage disequilibrium with allergen-specific high-responding IGHE genes and present the atopic phenotype of bronchial asthma, while the IGHG3(g/g)-IGHG1(a/a)-IGHG2(–n/–n) genes present the nonatopic phenotype of childhood asthma. The two genotypes with different amino acid epitopes of their constant heavy γ1, γ2 and γ3 chains presented qualitatively different IgG1, IgG2 and IgG3 molecules, respectively, and also different serum IgG1, IgG2 and IgG3 levels, together with different numbers of peripheral blood eosinophils and CD8 lymphocytes. The two IGHG genotypes represent different pathways of human immune regulation. An association of atopic IGHG genotype with other candidate genes for atopy could be suggested. [ABSTRACT FROM AUTHOR] |
