Triiodothyronine Affects the Phytohemagglutinin to Concanavalin A Proliferative Response Ratio in Sex-Linked Dwarf Chickens 1

Abstract

Euthyroid Cornell K strain and sex-linked dwarf (SLD) strain cockerels (which have abnormally low serum triiodothyronine concentrations) were supplemented with either 0,0.01, 0.1, or 1.0 ppm of triiodothyronine (T₃) in the diet. Peripheral blood lymphocytes (PBL) from these cockerels were obtained by slow-speed centrifugation (slow-spin-prepared PBL). The proliferative response of these PBL to phytohemagglutinin (PHA) and concanavalin A (Con A) was determined when the chicks were 6, 9, and 12 weeks of age. Con A responsiveness was also determined in 12-week-old cockerels using PBL which were separated on Ficoll (Ficoll-prepared PBL). Using slow-spin-prepared PBL, PHA, and Con A responsiveness increased in both strains with increasing levels of T₃ supplementation. This enhancing effect of T₃ was particularly evident in older cockerels. In 6- and 12-week-old SLD strain cockerels, the PHA: Con A response ratio was significantly (P < 0.05) lower than in K strain cockerels. At 12 weeks of age the PHA:Con A response ratio of the SLD strain was elevated to K strain control levels by T₃ supplementation. Therefore, the lower PHA:Con A response ratio in the SLD strain appears to be partially due to the existing peripheral hypothyroidism in this strain. Using Ficoll-prepared PBL, the effects of T₃ on Con A responsiveness differed from those observed when slow-spin-prepared PBL were used. From this study we conclude that T₃ supplementation affects mitogen responsiveness and the PHA:Con A response ratio. However, the effects of T₃ on mitogen responsiveness depend on the age of the chicken, the level of T₃ supplemented, the T cell population stimulated, and the method of lymphocyte enrichment.