Prevalence of thyroid autoantibodies in ambulatory elderly women.

Major improvements in thyroid autoantibody testing have now become widely available. Seventy-five elderly ambulatory women from a senior citizens' center (mean age 74.5 yrs) were studied to reassess the prevalence of thyroid autoantibodies and to demonstrate how such tests related to clinical signs and symptoms of thyroid disease. We used the enzyme-linked immunoassay (ELISA) technique for the measurement of autoantibodies to thyroglobulin (hTg) and thyroid peroxidase (hTPO) (as microsomal antigen), since ELISA systems are economical, highly sensitive and specific for population screening. Autoantibodies to hTPO (hTPO-Ab) were present in 44% and hTg autoantibodies (hTg-Ab) in 32% of the study group. Ten women (13.3%) had elevated thyrotropin (TSH) levels. An elevated serum TSH was associated with the presence of hTPO-Ab in varying concentrations. The mean TSH value of 7.2 microIU/mL in those women with hTPO-Ab was significantly higher than the mean of 4.7 microIU/mL found in those women without thyroid autoantibodies (p < 0.01). However, additional testing for hTg-Ab was of little clinical value. These data indicate the high prevalence of thyroid autoimmune disease in the elderly female population. We conclude that screening for thyroid dysfunction is best achieved by the measurement of serum TSH in all women over the age of 60 years. The measurement of hTPO-Ab, but not hTg-Ab, was helpful in confirming the cause of thyroid failure in the elderly female population.

Restricted heterogeneity and T cell dependence of human thyroid autoantibody immunoglobulin G subclasses.

Twenty-five sera from patients with autoimmune thyroiditis, positive for thyroglobulin (hTg) and/or thyroid microsomal autoantibodies (M-Ab), were assessed by specific micro-ELISA to determine thyroid autoantibody immunoglobulin G (IgG) subclass distribution. Of the 25 sera, 22 were positive for M-Ab. All but 1 sample had restricted heterogeneity confined to IgG1 and/or IgG4 subclasses. The contribution of each subclass to an individual autoantibody titer varied from 100% IgG1 to 100% IgG4. Sixteen of the 25 sera had detectable hTg-Ab, and the majority also were restricted to IgG1 and IgG4, with similar distributions occurring among subclasses. In all, only 5 sera had hTg/M-Ab in IgG subclasses 2 and/or 3. T cell control of pokeweed mitogen-stimulated IgG subclass secretion was analyzed using increasing numbers of T cells in ratios of T to non-T from 0:1 to 10:1. In normal subjects, IgG1, but not IgG 2, 3, or 4, had T cell dependence, as evidenced by enhancement and inhibition of IgG1 secretion as the number of T cells increased. T cell suppressor dysfunction was apparent in patients with autoimmune thyroiditis, as demonstrated by the reduced ability of patient T cells (n = 6), compared with normal T cells (n = 6), to suppress total IgG1 subclass secretion. These data indicate 1) restricted heterogeneity of human thyroid autoantibodies, principally to IgG1 and IgG4; 2) T cell dependence of only IgG1 secretion in vitro; and 3) a T cell defect in patients with autoimmune thyroid disease. The possibility of IgG4 thyroid autoantibodies being under less stringent T cell regulatory control questions the likely importance of thyroid-specific suppressor T cell dysfunction in the etiology of autoimmune thyroid disease.