Differential effects of thyroxine on immune development and autoimmune thyroiditis in the obese strain chicken

The effects of dietary thyroxine (T4) supplementation for specific periods on the early development of the primary lymphoid organs and spontaneous autoimmune thyroiditis (SAT) was examined in the Obese (OS) strain of chicken. Effects of the treatments on concentrations of serum growth hormone (GH) and testosterone were also determined. All treatment groups were examined at 6 weeks. T4 supplementation did not affect serum testosterone or GH concentrations. However T4 given for the first three weeks resulted in significantly increased bursa weights, no change in thymic weights, significantly decreased lymphoid infiltration of the thyroid and reduced thyroglobulin autoantibody levels (TgAAb). T4 supplementation for the full six weeks resulted in no change in bursal weight, significantly increased thymic weight, significantly decreased lymphoid infiltration of the thyroid, and reduced TgAAb. These results suggest that the effects of T4 supplementation on SAT and immune development are dependent on the interval during which it is administered and that testosterone and GH probably do not mediate these effects.