Circannual rhythm in natural killer activity and mitogen responsiveness of murine splenocytes

Seasonal variations were observed in murine splenic natural killer (NK) cell activity and also in murine lymphocyte responsiveness to mitogens, namely, concanavalin A, phytohemagglutinin, and lipopolysaccharide. The maximum and minimum splenic NK cell activities were observed in January-February and July-August, respectively. Conversely, maxima and minima of lymphoproliferative responses to all the three mitogens occurred in April-June and January-February, respectively. Such variations, when inferential statistics are used, appeared to be accounted for by circannual and other low-frequency (infradian) bioperiodicities. More specifically, the circannual rhythm in murine NK cell activity was demonstrated in data from a total of 356 mice collected over a period of 5 years. The various components of the immune system are characterized by a multifrequency time structure. The understanding of the organization of the immune system along the yearly scale may have bearings on that of the seasonal incidence of numerous infectious diseases and on the success/failure of immunotherapy.