Seasonal differences in the rhythmicity of human male and female lymphocyte blastogenic responses.

To test the hypothesis that there are circannual differences in mitotic activity in males and females, normal human peripheral blood lymphocytes were stimulated with suboptimal concentrations of Phytohemagglutinin (PHA), Concanavalin A (Con A) and Poke weed mitogen (PWM) over two summer/winter cycles. Lymphocyte responses for the entire population were significantly higher in the summer than in the winter. The same results were observed when responses were compared between a summer and a successive winter. However, when male and child-bearing age female responses were compared, females showed a higher significant difference for PHA and Con A between summer and winter, but not for PWM. These different responses due to season may reflect a relationship between the neuroendocrine and immune systems. At the cell level, these results suggest that an inherent difference exists between female and male lymphocytes and that these lymphocytes are sensitive to seasonal changes.