Future directions in exercise and immunology: regulation and integration.

Although it is difficult to predict future directions in a rapidly expanding field such as exercise immunology, recently published research along with that presented at this Symposium allow us to ask some key questions which may point to new directions: 1) Are athletes immunocompromised? Athletes are not clinically immunodeficient, yet endurance athletes are at increased risk of illness. Long-term prospective studies are needed to understand the relationship between infection, training variables and immune parameters. 2) Is downregulation of nonspecific immunity beneficial or harmful? In athletes, neutrophils appear to be downregulated, and this may alter resistance to illness. Alternatively, neutrophils are mediators of tissue damage during inflammation. Downregulation of neutrophil function may be protective by limiting chronic inflammation. In athletes, mild immunosuppression may reflect a compromise between the body's attempts to limit inflammation while maintaining immune function. 3) What mediates communication between events in skeletal muscle and the immune system? Leukocyte mobility is affected by metabolic and mechanical factors during exercise. Exercise increases cytokine levels in damaged skeletal muscle and expression of adhesion molecules. Future work is likely to focus on the role of cytokines and adhesion molecules in mediating exercise-induced changes in leukocyte mobility. 4) Can exercise training provide a "countermeasure" against immunosuppressive events? Moderate exercise training may have a role in stimulating the immune system during certain diseases (e.g., HIV-infection), immune dysfunction (e.g., chronic fatigue syndrome) or reduced responsiveness (e.g. aging, spaceflight). It is also likely that future study will apply molecular biology techniques to further identify mechanisms by which exercise influences immune function.