Effects of Environmental Temperature on Thymus and Spleen Weights and Lymphocytes in Mice

Thymus and spleen weights and lymphocytes in the blood were examined in mice transferred from 22°C to 12°C or 32°C environments. After the exposure to either environment, organ weights tended to decrease. In mice exposed to 12°C, the number of WBCs and mononuclear cells and the ratio and the number of T cells decreased on day 1 and/or 3 after the exposure. The number of B cells also declined on day 3, but the ratio of B cells increased on days 3 and 7. In mice exposed to 32°C, the number of WBCs and mononuclear cells and the number of T cells decreased on day 1 and increased on day 7 and/or 14. The ratio of T cells declined on days 1, 3 and 7, while that of B cells increased on day 3, and the number of B cells increased on day 7. These results show that wide variations in environmental temperature affect the weights of organs and the number of cells which act on immune responses in mice.