Age-related changes in specificity of human natural autoantibodies to thyroglobulin.

We have analysed the epitopic and idiotypic specificity of thyroglobulin antibodies in infants, young adults, aged subjects and pregnant women in order to evaluate the changes that occur in the autoantibody repertoire with age in physiological situations. No increase in IgG anti-Tg autoreactivity in whole serum and purified IgG from serum was observed with aging. However, IgG from elderly individuals exhibited increased reactivity, as compared to other groups of donors, against particular epitopes commonly recognized by both natural and disease-associated Tg-autoantibodies. The acquisition of a distinct epitopic reactivity in aged individuals suggests that qualitative rather than quantitative criteria could characterize alteration in regulation of the autoreactive B-cell repertoire that occurs with aging. No correlation was observed between the age of the donors and expression of a thyroid disease-associated idiotype (T44 Id) by hTg-autoantibodies. The expression of T44 Id on IgG obtained from serum of a small number of pregnant women may be an effect of the modifications of immune system function in pregnancy, which could lead to increased incidence of autoimmunity during pregnancy or in the post-partum period.