Effects of exercise on the macrophage MHC II response to inflammation

The purpose of this investigation was to determine the effects of different doses of exercise on the ability of Propionibacterium acnes (P. acnes) to induce major histocompatibility complex (MHC) II antigen expression on macrophages (M∅'s). Pathogen-free male Balb/c mice were exercised on a treadmill moderately (MOD, 15-17 m/min, 5% grade, 30 min/day) or exhaustively (EXH, 15-40 m/min, 5% grade, 2-4 hr/day) for a period of 7 days during P. acnes-induced inflammation. A control group (CON) consisted of animals exposed to the treadmill environment and handling. Sub-optimal (0.03 mg/g b.wt., i.p.) and optimal (0.08 mg/g b.wt.) doses of P. acnes were used to increase M∅ MHC II expression. Animals were sacrified on Day 7 and M∅'s were harvested by peritoneal lavage. Direct immunofluorescent staining was performed by incubating peritoneal exudate cells (10⁶) with an FITC-labeled anti-mouse MHC II (I-A(d)) antibody. Basal expression of MHC II was not affected by exercise. There were no significant differences among the groups in the percentage of M∅'s expressing MHC II at any dose of P. acnes. However, EXH significantly (p < 0.05) suppressed the expression (mean fluorescent intensity, MFI) of MHC II when compared to MOD (37.1 ± 1.95 [mean ± sem] vs 49.1 ± 2.15, p < 0.05) at the suboptimal P. acnes dosage. At the optimal P. acnes dose, both MOD and EXH significantly suppressed (27 ± 1.6, 25 ± 2.2 and 41.5 ± 3.2, for EXH, MOD, and CON, respectively, p < 0.0001) P. acnes-induced M∅ MHC II MFI. Plasma corticosterone was highly (r = -0.71, p = 0.001) inversely correlated with M∅ MHC II expression. However, exercise failed to affect P. acnes-induced production of interferon-γ. These data suggest that, dependent on the degree of stimulation, exercise can negatively affect M∅ expression of MHC II, an effect that may be detrimental to the M∅'s ability to present antigen to T lymphocytes.