Systemic inflammatory response to exhaustive exercise. Cytokine kinetics.

It has been documented that strenuous exercise not only induces pyrogenesis but also elicits mobilization and functional augmentation of neutrophils and monocytes whereas it suppresses cellular immunity leading to increased susceptibility to infections. As mediators of these phenomena, cytokines released into the circulation have been a recent focus of attention. Indeed, there are as many as one hundred original reports concerning exercise and cytokines, and half of them have been published in rapid succession from 2000, resulting in a tremendous accumulation of new knowledge within such a short term. The first aim of this review is to comprehensively summarize previous studies on systemic cytokine kinetics following exercise, with a special focus on reproducibility and quantitative comparison in human studies using specific immunoassays. Although tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 beta have traditionally been understood to be the main inducer cytokines of acute phase reactions, the majority of studies have shown that the circulating concentration of these cytokines is either unchanged following exercise, or exhibits relatively small, delayed increments. Plasma interferon (IFN)-alpha and IFN-gamma do not appear to change following exercise, whereas IL-2 decreases after endurance exercise. The small changes of these proinflammatory and immunomodulatory cytokines could well be mediated by anti-inflammatory cytokines such as IL-1 receptor antagonist (IL-1ra), IL-6 and IL-10 and cytokine inhibitors (cortisol, prostaglandin E2 and soluble receptors against TNF and IL-2), which are known to increase markedly in the circulation following endurance exercise. Moreover, it has been recently demonstrated that endurance exercise induces systemic release of granulocyte colony-stimulating factor (G-CSF), macrophage CSF (M-CSF), IL-8 and monocyte chemotactic protein 1 (MCP-1). Although the majority of available data have been obtained following prolonged exercise, it remains to be elucidated whether short-duration intensive exercise also causes rapid systemic cytokine release. In addition, there have been few studies that have simultaneously compared the extent of each cytokine response to exercise from a wider perspective. The second aim of this study was to examine possible changes of not only plasma but also urine concentrations of a broad spectrum of cytokines (16 kinds) following maximal exercise, including the time course of recovery. Although plasma TNF-alpha could not be detected throughout, it was present in urine 2 h after exercise. Plasma IL-1 beta rose significantly 2 h after exercise, but plasma IL-1 ra increased more rapidly and markedly than IL-1 beta, thus IL-1 bioactivity should be blocked at least in the circulation. Although there was only a trend toward increased plasma IL-6 concentrations after exercise, urine IL-6 rose significantly 1 h after exercise, indicating that IL-6 was released systemically but eliminated rapidly into the urine. Furthermore, it is shown for the first time that plasma and urine IL-4 concentrations were significantly elevated 2 h after exercise. Therefore, it is possible that anti-inflammatory cytokines might be released into the circulation as a regulatory mode of the cytokine network for adaptation against systemic inflammatory stress. Additionally, we have demonstrated that plasma concentrations of G-CSF, granulocytemacrophage CSF (GM-CSF), M-CSF, IL-8 and MCP-1 increased immediately after short-duration exercise and that the urine concentrations of these cytokines were much more pronounced than the changes observed in plasma. In conclusion, cytokines that are considered to induce systemic bioactivity following exercise are not only anti-inflammatory cytokines but also colony-stimulating factors and chemokines, which were secreted in an earlier phase of exercise without the kinetic involvement of traditional proinflammatory cytokines. Although the wider physiological and pathological implications are still not clearly understood, these cytokine kinetics may partly explain suppressed cell-mediated immunity and increased allergic reactions derived from a lower type-1 to type-2 cytokine ratio, along with mobilization and functional augmentation of neutrophils and monocytes. The sources and stimuli of cytokine production are not fully elucidated at present, but several hypotheses based on recent experimental evidence are discussed in this review herein.