Regular Intense Exercise Poses a Challenge to the Immune System
Exercise elicits an increase in the numbers of circulating lymphocytes and lymphocyte subsets (including NK cells) which is followed by a decrease in the numbers of cells during recovery from exercise; this lymphocytopenia appears to be due to a decrease in the percentage of type 1 T cells and NK cells in the circulation at this time. A decrease in mitogen-stimulated T cell proliferation and T cell production of IL-2 and IFN-gamma is reported immediately after acute, intensive exercise. NK cell cytolytic activity per cell (NKCA) does not appear to change much after exercise unless the bout was prolonged, intense and stressful, in which case NKCA can be depressed for several hours. Resting immune function is not very different in athletes compared with non-athletes. However, periods of intensified training in already well trained athletes can result in a depression of immunity in the resting state which may be due to the cumulative effects of repeated bouts of intense exercise with the consequent elevation of stress hormones, particularly cortisol and anti-inflammatory cytokines (e.g. IL-6, IL-10, IL-Ira) causing temporary inhibition of type 1 T cell cytokine production with a relative dampening of the type I (cell-mediated) response.
Gleeson M, Bishop NC. The T cell and NK cell immune response to exercise. Ann Transplant. 2005 October School of Sport and Exercise Sciences, Loughborough University, Leicestershire, England