The Sardinian Autoimmunity Study: 3. Studies on circulating antithyroid antibodies in Sardinian schoolchildren: relationship to goiter prevalence and thyroid function.

The relationship among iodine intake, goiter prevalence, and thyroid autoimmunity remains controversial. In the present article, we report the prevalence of antithyroid antibodies (ATA) in relation to iodine intake, frequency of goiter, and thyroid function in a large group of Sardinian schoolchildren living in areas with borderline iodine sufficiency, or mild to moderate iodine deficiency. A total of 8,040 schoolchildren (4,194 males, 3,846 females, ages 6-15 years) from 29 communities were examined between 1986-1994. Thyroid size was assessed by palpation, according to the Pan American Health Organization (PAHO) criteria. In all cases antimicrosomal (MAb) or antithyroid peroxidase antibodies (TPOAb) and thyrotropin (TSH) were assayed. Urinary iodine was determined in a subgroup of 820 children. ATA was detected in 235 (2.92%) sera (88 males, 2.12%; 147 females, 3.82%; chi2 = 20.41, p < 0.0001). ATA prevalence ranged between 0.0%-7.3% in the 29 communities without any geographical correlation with goiter prevalence and urinary iodine excretion. However, ATA was more frequently detected in goitrous children, especially in females. The presence of ATA was not age-dependent in males, whereas a significant increase of ATA was observed in females older than 11 years of age. Seventy-seven (0.96%) children showed borderline to slightly increased serum TSH (>5.2-32 mU/L). Increased serum TSH concentration was more frequently found in children with ATA, especially at higher titers. In summary, our study in Sardinian schoolchildren indicates: (1) ATA display geographical heterogeneity, which seems to be unrelated to goiter prevalence and/or to iodine supply; (2) ATA are more frequently detected in females older than 11 years of age, suggesting that puberty has a role in determining the predominance in females of thyroid autoimmunity; (3) although most goitrous children are ATA-negative, the prevalence of ATA is increased in children with enlarged glands; (4) ATA is associated with an increased prevalence of subclinical hypothyroidism.

Circulating soluble IL-2 receptor levels are low in patients with hypothyroid autoimmune thyroiditis.

In hypothyroid patients serum soluble IL-2 receptor levels showed scattered and conflicting results. In our report we studied circulating soluble interleukin 2 receptors in 22 patients with hypothyroid autoimmune thyroiditis before L-thyroxine treatment and when the patients became euthyroid. The mean of soluble Interleukin 2 receptor levels in the hypothyroid state was 48.6 pmol/l (95% confidence interval, 45.6-51.5) statistically lower than in the controls (95% confidence interval, 86.4 pmol/l, 83.3-89.4) (p < 0.0001). When the patients became euthyroid during L-thyroxine treatment, soluble Interleukin 2 receptor levels increased, showing mean values comparable to the controls. A positive high correlation (p < 0.001) was observed between soluble Interleukin 2 receptor levels and thyroxine free levels in the hypothyroid as well as in the euthyroid state and between soluble Interleukin 2 receptors and the mean weekly L-thyroxine dose. Our study confirmed that in the hypothyroid state, the behaviour of soluble Interleukin 2 receptors is anomalous as compared to other autoimmune diseases. In fact a strict relationship exists between the levels of thyroid hormones and soluble Interleukin 2 receptors but not between the latter and antithyroid antibodies. These results agree with those supporting a role for thyroid hormones in the regulation of the immune system. They also suggest that the measurement of soluble Interleukin 2 receptors could be used as a marker of the peripheral action of thyroid hormones.