Prolonged high-intensity exercise induces fluctuating immune responses to herpes simplex virus infection via glucocorticoids.

Background: Epidemiologic studies have yielded conflicting results regarding the influence of a single bout of prolonged high-intensity exercise on viral infection.

Objective: We sought to learn whether prolonged high-intensity exercise either exacerbates or ameliorates herpes simplex virus type 2 (HSV-2) infection according to the interval between virus exposure and exercise.

Methods: Mice were intravaginally infected with HSV-2 and exposed to run on the treadmill.

Results: Prolonged high-intensity exercise 17 hours after infection impaired the clearance of HSV-2, while exercise 8 hours after infection enhanced the clearance of HSV-2. These impaired or enhanced immune responses were related to a transient decrease or increase in the number of blood-circulating plasmacytoid dendritic cells. Exercise-induced glucocorticoids transiently decreased the number of circulating plasmacytoid dendritic cells by facilitating their homing to the bone marrow via the CXCL12-CXCR4 axis, which led to their subsequent increase in the blood.

Conclusion: A single bout of prolonged high-intensity exercise can be either deleterious or beneficial to antiviral immunity.