The effects of exercise on macrophage function

Abstract

Innate immunity is our first line of defense against infectious pathogens. One of the major constituents of the innate immune system is macrophages that perform important phagocytic, regulatory and antigen presentation functions. Physically active individuals are reportedly less susceptible than sedentary individuals to viral and bacterial infections, suggesting that exercise improves immune function. Exercise increases the release of catecholamines, glucocorticoids and other factors that have immunomodulatory effects. For example, proinflammatory cytokine production from macrophages was inhibited by β2-adrenergic receptor (β2AR) agonist catecholamines, but exercise training down-regulated the expression of β2AR in macrophages, improving innate immune functions. In addition, the generation of suppressor macrophages by glucocorticoids that are normally induced during acute cold stress was inhibited in swimming-trained mice. Also, an inactive lifestyle leads to the accumulation of visceral fat, which is accompanied by adipose tissue infiltration by pro-inflammatory immune cells, mainly macrophages, and the development of a low-grade systemic inflammatory state. Exercise decreases chronic low-grade systemic inflammation and improves insulin sensitivity in obese individuals. Although the mechanisms behind these favorable effects of exercise are not fully understood, recent studies have shown that exercise training prevents adipose tissue infiltration by pro-inflammatory macrophages and that ghrelin expressed in macrophages functions as a mediator of the anti-inflammatory effects of exercise training. In this Review, the authors focus on the known mechanisms by which exercise exerts its effects on macrophages, and discuss the implications of these effects for the prevention and treatment of disease.

Keywords

• exercise training
• macrophage
• innate immunity
• stress
• inflammation