Adaptation of macrophages to exercise training improves innate immunity

The effects of 3-week exercise training on the functions of peritoneal macrophages from BALB/c mice were investigated. Lipopolysaccharide (LPS)-stimulated nitric oxide (NO) and proinflammatory cytokine production in macrophages from trained mice was markedly higher than those from control mice. Meanwhile, exercise training decreased the steady state level of β₂-adrenergic receptor (β₂AR) mRNA in macrophages. Overexpression of β₂AR in the macrophage cell line RAW264 by transfecting with β₂AR cDNA suppressed NO synthase (NOS) II expression but dose not influenced proinflammatory cytokine expression. When expression of transfected β₂AR in RAWar cells was downregulated by a tetracycline repressor-regulated mammalian expression system, NOS II mRNA expression was significantly increased; this suggested that the changes in the β₂AR expression level in macrophages associated with exercise training play a role in the regulation of NO production following LPS stimulation. These findings indicate that exercise training improves macrophage innate immune function in a β₂AR-dependent and -independent manner.