Exhaustive exercise reduces TNF-α and IFN-α production in response to R-848 via toll-like receptor 7 in mice

Abstract

Stressful exercise results in temporary immune depression. However, the impact of exercise on the immune responses via toll-like receptor (TLR) 7, which recognizes the common viral genomic feature, single-stranded RNA, remains unclear. To clarify the effect of stressful exercise on immune function in response to viral infection, we measured the changes in the plasma concentration of tumor necrosis factor (TNF)-α and interferon (IFN)-α, which are induced downstream from the TLR-ligand interaction, in exhaustive-exercised mice immediately after treatment with the imidazoquinoline R-848, which can bind to and activate TLR7. Both exhaustive-exercised (EX) and non-exercised (N-EX) male C3H/HeN mice were injected with R-848 (5 mg kg(-1)), and blood samples were collected. In addition, RAW264 cells, which are mouse macrophage cells, were cultured 30 min after epinephrine (10 μM) or norepinephrine (10 μM) treatments, and were then stimulated with R-848 (10 μg ml(-1)). In addition, the effect of propranolol (10 mg kg(-1)) as blockade of β-adrenergic receptors on R-848-induced TNF-α and IFN-α production in the exercised mice was examined. Both the TNF-α and IFN-α concentrations in the plasma of EX were significantly lower than those in the plasma of N-EX after R-848 injection (P < 0.05 and P < 0.01, respectively), although the R-848 treatment increased the plasma TNF-α and IFN-α concentrations in both groups (P < 0.01, respectively). The R-848-induced TNF-α production in RAW264 cells was significantly inhibited by epinephrine and norepinephrine pre-treatment, although IFN-α was not detected. The propranolol treatment completely inhibited exercise-induced TNF-α and IFN-α suppression in response to R-848 in the mice. These data suggest that EX induces a reduction in TNF-α and IFN-α production in response to R-848, and that these phenomena might be regulated by an exercise-induced elevation of the systemic catecholamines.

Fig. 1

Effect of exhaustive exercise on plasma TNF-α concentrations in mice in response to R-848. Open circles represent the values in the non-exercised mice (N-EX, n = 14), and the closed circles represent these values in exercise mice (EX, n = 11). The plasma TNF-α concentration in the EX group was significantly lower than that in the N-EX group at 1 and 3 h after R-848 (5 mg kg⁻¹, i.v.) injection (P < 0.05, respectively). *P < 0.05 vs. N-EX at each point and ^## P < 0.01 vs. the value at Pre in each group

Fig. 2

Effect of exhaustive exercise on plasma IFN-α concentrations in mice in response to R-848. The open circles represent those values in non-exercised mice (N-EX, n = 14), and the closed circles show these values in exercised mice (EX, n = 11). The increase in the IFN-α concentration in plasma was attenuated by exhaustive exercise 1 h after R-848 injection (P < 0.01). **P < 0.01 vs. N-EX at each point and ^## P < 0.01 vs. the value at Pre in each group

Fig. 3

Effect of epinephrine (E) and norepinephrine (NE) treatment on TNF-α and IFN-α production in response to R-848 in RAW264 cells. Cells (2 × 10⁴ well⁻¹) were incubated for 6 h with or without R-848 (10 µg ml⁻¹) 30 min after treatment with E (10 µM) or NE (10 µM). The TNF-α production in both E- and NE-treated cells was significantly lower than that in vehicle (V)-treated cells after R-848 stimulation (P < 0.01, respectively). **P < 0.01 vs. V with R-848 and ^## P < 0.01 vs. E with R-848. IFN-α was below the detection limits for all three treatments

Fig. 4

Effect of the β-adrenagic receptor antagonist propranolol (Prop) on plasma TNF-α (a) and IFN-α (b) concentrations in response to R-848 in exhaustive-exercised mice. Mice were treated with Prop (10 mg kg⁻¹, i.p.) 30 min before the exercise (Prop+EX). Plasma TNF-α and IFN-α concentrations in the EX group were significantly lower than those in the N-EX group 1 h after R-848 (5 mg kg⁻¹, i.v.) injection (both **P < 0.01), but there were no significant differences between the plasma cytokine concentrations in the Prop+EX and the N-EX groups in response to R-848. ( ): n