How does exercise affect leukocyte populations and/or activity?

How does exercise affect leukocyte populations and/or activity?

When dealing with endurance exercise there are generally three levels of exercise intensity: low, moderate, and high. These levels correspond to an oxygen consumption rate (VO2) and/or level of sustained heart rate during exercise. Most health benefits from exercise comes from moderate (<1 hr, 3-5 days/wk ( <65% VO2max) to high intensity (>1 hr, 5-7 days/wk >65% VO2max) exercise.
How does moderate and high intensity bouts effects neutrophils (PMN)?
Neutrophil counts are higher in athletes but the activity of the neutrophils are diminished (10). Acute bouts of exercise induces an increase in PMN numbers. This has been directly correlated with the intensity and duration of the exercise bout. Cycling at 60% VO2max for one hour results in PMN's being primed for their respiratory burst for up to 6 hours post-exercise (10). Moderate exercise also causes a increase in high activity cells which possibly increases PMNs phagocytic and killing abilities (10).
High intensity training depresses some neutrophil functions chronically with possible increases in their killing ability. This level of exercise results in a primed PMN chemotactic response to super oxides and will lead to a 2 fold increase in PMN phagocytic capacity (10). In addition, intense training decreases the adhesive capacity by 3 fold; however, this information is questionable. The decrease observed may result in a decreased ability of PMN's to extravasate into tissue at the sight of infection, leading to a possible decreased ability to rid the body of the infection. The significance of these occurrences is still unknown (10).
What does moderate and high intensity bouts affect natural killer cells (NK)?
When comparing athletes to non-athletes, regardless of age, the natural killer cell activity is enhanced in the athletic population. Evidence suggests that moderate intensity exercise increases the numbers of NK cells and the number of circulating lymphocytes (2,5). NK activity peaks immediately following exercise and drops to subnormal levels over the next 120 minutes. This activity level gradually recovers over the next 20 hours. The long-term response of NK cells to exhaustive exercise is less favorable because there is a possible down-regulation of NK activity. Evidence that low intensity exercise increase the numbers of NK cells and the number of circulating lymphocytes(2, 5).
Heavy training induces a prolonged depression of the NK/ IL-2 system, and this change is probably responsible for the vulnerability to acute infection associated with both single bouts of very strenuous physical activity and chronic over-training (8). It has been clearly shown in several studies that the incidence of highly trained athletes contracting a upper respiratory infection (URTI) is increased following marathons and other long endurance events where athletes are performing for long time periods at a high percentage of their VO2max (7). As little as 90-120 minutes of exercise at 60% VO2 max can lower peripheral blood NK activity for a week or more (8). NK cytolytic activity has been found to be poor in AIDS patients, and in such individuals cytolysis could be augmented by infusion of IL-2 because IL-2 could be the immediate signal to induce the production of cytotoxic factors by the NK cells (8).
What does moderate and high intensity bouts affect lymphocyte populations activity level?
Overall, the innate immune response responds to intense exercise but the adaptive immune response is largely unaffected. When considering just the older population, T cell function is enhanced in elderly trained individuals when compared to untrained individuals of the same age (4). One study examined a 15 week exercise training protocols effect on the immune cells of subjects. The exercise group had significant decreases in lymphocyte percentage, however no effect was observed on the total leukocyte count, spontaneous blastogenesis, T helper/inducer cell number, T cytotoxic/suppressor cell number or helper/suppressor T cell ratio (4). In other studies, T-cell response has been reported to decrease for up to 3 hours after a marathon but not shorter distance running. This will also vary with fitness level. It is unknown whether or not this will influence susceptibility to infection (2).