Effects of thyroxine on T-cell counts and tumour cell rejection in mice

In an attempt to study the effect of thyroxine on peripheral T-cell (thymus derived lymphocyte) counts or immunological functions, inbred C3H/He mice (8-10 weeks old) were injected subcutaneously with thyroxine for more than 3 months. After treatment for 3 months the mice were examined for peripheral T-cell counts, thymic incorporation of tritiated thymidine and rejection of tumour transplants. The number of T-cells was counted by the indirect immunoflourescence method using anti-thetaC3H serum after separation of lymphocytes on "Ficoll-Conray". It was revealed that the peripheral counts of both lymphocytes and T-cells were increased in the thyroxine treated group as compared with the control group, as was reported in the patients with Graves' disease. Thymic incorporation of tritiated thymidine was also found to be significantly increased in the thyroxine treated group. In addition, in order to study T-cell activity of the host, thyroxine treated and control mice were challenged with Ehrlich carcinoma cells at several concentrations (10(2), 10(4) and 2 x 10(6) per mouse). It was found that rejection of tumour transplants was significantly enhanced in the T-cell rich mice. Thus, it is possible that throxine affects peripheral T-cell counts and enhances immunological functions of the host.