Voluntary Exercise Alters Adaptive Immunity Prior to Injury

OBJECTIVE: Exercise provides a neuroprotective role in the setting of cerebral infarct. However, the exact mechanism for this protection is unclear. This study established an exercise preconditioning protocol to test the hypothesis that exercise mediates protection from stroke by altering the immune profile prior to injury to reduce inflammation post-infarct. MATERIALS/METHODS: In our first trial, a three week exercise preconditioning protocol was established using nine C57 mice that endogenously expressed green fluorescent protein (GFP) under the PLP promoter. This biomarker was used to identify oligodendrocyte precursor cells (OPC) to qualify their relationship with voluntary exercise. Exercise activity was recorded and tissues were collected for histological and serological analysis. Analysis of histological sections acquired through Nanozoomer imaging was performed using an unbiased quantification (Stereo Investigator). Ten Swiss Webster (SW) mice with no endogenous fluorescence were used in the subsequent trial. Following sacrifice of the SW mice, samples of the spleen and peripheral blood were collected and analyzed by flow cytometry and microarray was used to analyze resident B cell expression (IPA software). Standard ELISA analysis of peripheral blood was also used for all trials. Significance was determined using t-test or ANOVA. RESULTS: Voluntary exercise in PLP-EGFP mice correlated with a trend increase in OPCs as well as a trend increase in cortical angiogenesis (p=0.06). However, voluntary exercise did not increase hippocampal neuron counts. Voluntary exercise in SW mice showed decreases in percent and raw number of splenic neutrophils and CD8+ T cells (both p<0.01), with a concomitant increase in B cell representation (p<0.05). Peripheral blood samples demonstrated a decrease in percent CD4+ T cells (p<0.01) and decrease in CCL2 (p<0.05) and VEGF (p<0.01) protein. Microarray showed a significant upregulation of 1844 genes and significant downregulation of 1333 genes in the resident splenic B cells of SW exercise mice over the sedentary controls. CONCLUSION: Three weeks of voluntary exercise in mice results in a change in the immune profile prior to an injury occurring. Downregulation of neutrophils, cytotoxic T cells, and CCL2 suggest that this alteration in immunity is anti-inflammatory. Microarray analysis of isolated B cells showed an upregulation of genes associated with lymphocyte maturation and differentiation, with simultaneous downregulation of genes responsible for apoptosis and B cell death. Further studies will determine the significance of these immune adaptations and their mechanistic role in decreased deficits following neurovascular injury.