The effect of the thyroidal state on the immunological state of the chicken

Effects of the thyroidal state on certain immunological parameters were studied in four groups of male White Leghorn chicks. One group was fed with commercial chick mash and served as control, the second was supplemented with 0.1% Propylthiouracil (PTU) in food, the third was supplemented with 0.025% thyroxine in food, and the fourth was supplemented with 0.1% PTU and 0.025% thyroxine. Treatment with PTU (29 days) resulted in hypothyroidism evidenced by low T₄ level, decreased oxygen consumption rate and decreased weight gain. Thyroxine treated group reached hyperthyroidism shown by high T₄ level and increased oxygen consumption rate. When all chicks were immunized with SRBC, hemagglutinating antibody titer of PTU treated group was significantly lower than that of the other group while thyroxine treatment resulted in increased, but statistically not significant titers. At 36 days of age the chicks were killed. PTU treated group exhibited decreased thymus, spleen and bursa weights and low ³H thymidine incorporation after Con A stimulation of both spleen and thymus cells. Thyroxine treatment resulted as well in low ³H thymidine incorporation. These findings indicated that hypothyroidism depressed the immunological system, while hyperthyroidism had no effect on antibody formation but depressed reactivity to Con A stimulation.