EXERCISE-INDUCED IMMUNOMODULATION - POSSIBLE ROLES OF NEUROENDOCRINE AND METABOLIC FACTORS

Acute muscular exercise induces an increased neutrophil count concomit ant with recruitment of natural killer (NK), B and T cells to the bloo d as reflected by an elevation in the total lymphocyte count. Meanwhil e, following intense exercise of long duration the lymphocyte count de clines, non-MHC-restricted cytotoxicity is suppressed, but the neutrop hil concentration increases. In relation to eccentric exercise involvi ng muscle damage, the plasma concentrations of interleukin-1, interleu kin-6 and the tumor necrosis factor are elevated. In this review we wi ll propose a model based on the possible roles that stress hormones pl ay in mediating the exercise-related immunological changes: adrenaline and to a lesser degree noradrenaline are responsible for the immediat e effects of exercise on lymphocyte subpopulations and cytotoxic activ ities. The increase in catecholamines and growth hormone mediate the a cute effects of exercise on neutrophils, whereas cortisol may be respo nsible for maintaining lymphopenia and neutrocytosis after exercise of long duration. Lastly, the role of beta-endorphin is less clear, but the cytokine response is closely related to muscle damage and stress h ormones do not seem to be directly involved in the elevated cytokine l evel. Other possible mechanisms of exercise-induced immunomodulation m ay include the so-called glutamine hypothesis, which is based on the f act that skeletal muscle is an important source of glutamine productio n and that lymphocytes are dependent on glutamine for optimal growth. Furthermore, physiological changes during exercise, e.g. increased bod y temperature a nd decreased oxygen saturation may also in theory cont ribute to the exercise-induced immunological changes.