Changes in T cell populations due to local irradiation of a portion of the maxilla in mice

The aim of this study was to investigate the changes in the immune organs after head and neck irradiation. The numbers of lymphocytes in peripheral blood, the spleen and the thymus following local irradiation of a portion of the maxilla in mice were studied using three-color fluorometry and were compared with a non-irradiation group. In the peripheral blood, the absolute numbers of T cells, CD4+SP cells and CD8+SP cells decreased after irradiation, and the period of the decrease was longer than the decreases in number of leukocytes and lymphocytes. The ratio of CD4+SP cells showed a significant decrease, and the ratio of CD8+SP cells showed a significant increase 1 day after irradiation. In the spleen, the absolute number of T cells, the radio of CD4+SP and CD8+SP cell subsets showed a decrease, and the period of the decrease was longer than the decrease of the wet-weight of the spleen, and also longer than the decrease of the number of leukocytes. The number of CD4+SP cells showed a signigicant increase, and CD8+SP cells showed a significant decrease 21 days after irradiation. In the thymus, the absolute number of TCR αβ-thymocytes did not show a significant decrease. However, the number of DN thymocytes showed a marked decrease. These results indicate that the numbers of T cells in peripheral blood, the spleen and the thymus change immediately after irradiation, and the numbers of lymphocytes and the T cells in the spleen recover more slowly than that in the peripheral blood. As lymphoid tissues showed the suppression of immunological response for a long period, it was suggested that lymphoid tissues have to be observed carefully after irradiation to prevent cancer metastasis. (K.H.)