Effects of mental arithmetic stress on blood cell counts and the immune system.

To determine whether acute mental stress alters the composition of peripheral blood cells or components of the immune system, we determined blood cell counts and leukocyte differential counts, and examined lymphocyte subsets, before, during, and after 10 min. of mental arithmetic in 20 healthy female students. During mental stress the absolute number of leukocytes, lymphocytes, CD8+ cells, and CD16+ cells increased significantly, and the rate of CD8+ cell increase was higher than CD4+ cell increase. Therefore the CD4+/CD8+ ratio decreased significantly during mental stress. Erythrocyte counts, hemoglobin concentrations and packed cell volumes remained unchanged during and after mental stress. These results demonstrate that acute mental stress is associated mainly with rapid peripheral blood lymphocyte changes, including the release of CD8+ and CD 16+ cells into circulation. The absence of significant increases in erythrocyte counts, hemoglobin concentrations, and packed cell volumes during stress indicates that changes in lymphocyte composition cannot be explained by the hemoconcentration. Thus, acute mental stress has a detectable influence on peripheral blood cell counts and the immune system.