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-ΘC3H 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 (102, 104 and 2 × 106 per mouse). It was found that rejection of tumour transplants was significantly enhanced in the T-cell rich mice. Thus, it is possible that thyroxine affects peripheral T-cell counts and enhances immunological functions of the host.

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In order to elucidate the nature of the megaloblastic lesion at the cellular level, DNA, RNA, and protein synthesis was studied in megaloblasts of pernicious anemia. While microphotometric estimation of DNA content showed an increase in cells with DNA values ranging around the 4c value, autoradiographic studies with H3-thymidine indicated, rather, a decreased ability to synthesize DNA. Combined microphotometric and autoradiographic studies suggested the impaired DNA synthesis with occasional arrests of synthesis, as well as the prolongation of the S period with or without the prolongation of the G2 period. On the other hand, active incorporation of H3-uridine and H3-leucine indicated active or unaffected RNA and protein synthesis. Vitamin B12 treatment rapidly corrected these aberrant patterns of synthesis. The significance of these findings has been discussed in relation to the mechanism of megaloblastic hemopoiesis.

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