VARIATIONS IN ACTIVITY OF THE HUMAN NATURAL ANTI-GAL ANTIBODY IN YOUNG AND ELDERLY POPULATIONS

Background. Anti-Gal,is a natural antibody which constitutes approxima tely 1% of circulating IgG in humans and which interacts specifically with the mammalian carbohydrate epitope Gal alpha 1-3Gal beta 1-4GlcNA c-R (termed the alpha-galactosyl epitope). The purpose of this study w as to determine whether there are age-associated changes in the affini ty of anti-Gal in elderly individuals. Methods, The age-associated var iations in affinity of anti-Gal were determined by the extent of this antibody binding to solid-phase alpha-galactosyl epitopes (mouse lamin in) in ELISA, performed at various serum dilutions with serum samples from 140 elderly and 127 young individuals. The data were expressed as the mean of optical density (O.D.) values measured at serum dilutions of 1:40, 1:80, and 1:160, and correlated with the affinity of anti-Ga l as measured in equilibrium dialysis. Results. The proportion of indi viduals with low-affinity anti-Gal is sixfold higher in the elderly th an in the young population. Whereas low-affinity binding of anti-Gal ( mean O.D. value less than or equal to 1.0) was observed in only 6% of the young population, as many as 35% of the elderly population display ed such low-affinity anti-Gal. Anti-Gal affinity in ELISA assay correl ated with the affinity of this antibody as measured in equilibrium dia lysis. Conclusion. The proportion of individuals with low affinity ant i-Gal increases in the elderly population in comparison with the young population. The possible molecular mechanisms which may result in the age-associated decrease in the antibody affinity are discussed.