Background: Patients with major depressive disorder (MDD) may display elevated plasma levels of pro-inflammatory substances. Although the underlying mechanisms are unknown, inflammation has been proposed to play a direct role in the generation of depressive symptoms. Skeletal muscle is a potent producer of cytokines, and physical exercise has been suggested to alleviate symptoms of depression. In this study we therefore addressed the question of whether MDD patients display altered levels of pro-, anti-inflammatory and regulatory factors in the blood in response to acute exercise.

Methods: Eighteen MDD patients and 18 healthy controls performed a maximal-workload exercise challenge. Blood samples were taken before the test, at sub-maximal and maximal workload, as well as 30 and 60 min after testing. The plasma levels of SAA, TNF-alpha, S-VCAM, S-ICAM, CRP, IFN-gamma, IL-1beta, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12 and IL-13 were assayed using multiplex sandwich ELISA.

Results: Exercise-induced significant changes in the plasma levels of inflammatory substances in both MDD patients and controls. IL-8, IL-6 and TNF-alpha increased, and IL-4 decreased during the challenge in both groups. In addition, IFN-gamma decreased in the controls. There was a significant difference in IL-6 reactivity between the groups at the sub-max timepoint.

Limitations: Group sizes are comparably limited.

Conclusion: Exercise induces changes in the blood levels of cytokines in unmedicated MDD patients. Whether these changes affect symptoms of depression should be evaluated in long-term studies of the anti-depressive effects of exercise.