SEASONAL-VARIATION IN PROLIFERATIVE RESPONSE AND SUBPOPULATIONS OF LYMPHOCYTES FROM MICE HOUSED IN A CONSTANT ENVIRONMENT

A seasonal variation in the proliferative response to mitogens and in the proportion of splenic lymphocyte subpopulations was found in mice housed in a constant environment. The lymphoproliferative responses to T-cell and B-cell mitogens reached maximum values in autumn and summe r. Identification of lymphocyte subpopulations by how cytometry demons trated that the proportion of T cytotoxic-suppressor (Tcs) lymphocytes was significantly higher in autumn and summer than in spring and wint er. However, the proportion of B lymphocytes was significantly lower i n spring than in the other three seasons, whereas the proportions of T and T helper (Th) cells did not show any seasonal variation. On the o ther hand, we observed a significant correlation between the level of mitogenic responsiveness and the proportion of Tcs cells, but not betw een the former and the proportions of B, T or Th cells. These data sug gest that the seasonal variation in murine lymphoproliferative respons es may depend on the cyclic changes in the proportion of Tcs lymphocyt es; these changes, in turn, may be predetermined by the inherent inter nal biological rhythms of the animal.