Effects of thyroid hormones on humoral and cell-mediated immune responses in the domestic fowl (Gallus domesticus).

We investigated the effect of raising and lowering circulating thyroid hormones in young domestic fowl on antibody production and the responses of peripheral blood lymphocytes (PBL) to the mitogens concanavalin A (con A) and phytohaemagglutinin (PHA). Circulating thyroid hormones were reduced by treatment with the goitrogen, methimazole, and raised by giving implants containing thyroxine (T4) and/or triiodothyronine (T3). Raising or lowering circulating thyroid hormones had no significant effect on peak antibody titers, though the decline in titer was slower in goitrogen-treated birds. Lowering circulating thyroid hormones caused a significant increase in the response to con A that was prevented by hormone replacement. There was no effect on the response to PHA and raising circulating hormones had no effect on the responses to con A or PHA. It is suggested that stress-induced changes in thyroid hormones could modulate cell-mediated immune responses.