Intracellular mechanisms responsible for exercise-induced suppression of macrophage antigen presentation

In a previous study, we demonstrated that exhaustive exercise suppressed pe ritoneal macrophage antigen presentation (AP). In this study, we explored t he intracellular mechanism(s) responsible for this suppression. Pathogen-fr ee male BALB/c mice (8 +/- 2 wk) were randomly assigned to either home cage control (HCC) or exhaustive exercise stress (Exh, 18-30 m/min for 3 h/day) treatment groups. The mice underwent treatments for a period of 4 days dur ing induced peritoneal thioglycollate inflammation. Elicited macrophages we re harvested, purified, and incubated with chicken ovalbumin (C-Ova, 2.5 an d 10 mg/ml) for 18 h. After macrophages were washed, they were cocultured w ith C-Ova-specific T cells for 48 h at which time the supernates were harve sted and analyzed via ELISA for interleukin (IL)-2 as an indication of macr ophage AP. There was no significant (P > 0.05) difference in macrophage AP between cells fixed with paraformaldehyde vs. those that remained unfixed, suggesting that Exh did not affect production of soluble factors influencin g macrophage AP (i.e., IL-1, IL-4, PGE(2)). The ability of macrophages to g enerate C-Ova immunogenic peptides was analyzed using FITC-labeled C-Ova, w hich shows fluorescence only when degraded intracellularly. There was a sig nificant (similar to 20%, P < 0.05) suppression in fluorescence in the Exh compared with HCC, indicating a possible defect in the ability of macrophag es from Exh to degrade C-Ova into immunogenic peptides. Macrophages were al so incubated with C-Ova immunogenic peptide in a manner identical to that f or native C-Ova. We found a similar suppression (similar to 22-38%, P < 0.0 5) in macrophage AP using a C-Ova peptide when compared with native C-Ova i n the Exh group, indicating reduced major histocompatibility complex (MHC) II loading and/or C-Ova-MHC II complex cell surface expression. In conclusi on, these data indicate an intracellular defect in the macrophage antigen p rocessing pathway induced by Exh.