Moderate exercise early after influenza virus infection reduces the Th1 inflammatory response in lungs of mice

We have previously shown that moderate exercise significantly increased survival after influenza virus (A/PR/8/34) infection in mice. We hypothesized that this brief duration of exercise would either increase innate immune defences and/or shift the immune response from a Th1 inflammatory to a Th2 anti-inflammatory response resulting in decreased lung pathology. Adult male BALB/cByJ mice (5-6 months old) were infected with 50 microL of A/PR/8/34 virus (40HAU) intranasally and randomized to either an exercise (EX) or sedentary (SED) group. EX mice performed 20-30 min of moderate exercise (8-12 m/min) on a motorized treadmill 4 hr post-infection and then exercised similarly for 4 consecutive days. SED mice were exposed to similar environmental conditions but did not exercise. Mice from both EX and SED groups were sacrificed 1, 3, or 5 days post-infection (p.i.) and lungs, mediastinal lymph nodes (MLNs) and spleens were harvested. EX significantly reduced total cellular infiltration and IFN-gamma gene expression in lungs at Days 3 and 5 p.i. and there was a qualitative shift in the expression of cytokines in the lung from a Th1 to a Th2 response. There was also a tendency toward a reduction in influenza M1 protein mRNA expression. There was no difference in IFN-beta protein levels between groups. These data suggest that moderate exercise when applied early after infection shifts the immune response away from a Th1 profile in mice infected with influenza virus. This exercise-induced shift in immune response may be responsible for improved survival after influenza virus infection.