Neutrophil and monocyte responses to downhill running: Intracellular contents of MPO , IL ‐6, IL ‐10, pstat3, and SOCS 3

High‐intensity exercise results in immune activation. This study determined whether (a) there is concordance between serum MPO and neutrophil and/or monocyte intracellular MPO content; (b) peripheral blood mononuclear cells respond to inflammatory interleukins ( ILs ) by increasing intracellular signaling. Healthy male ( n  = 12) volunteers participated in high‐intensity running (12 × 5 min, 10% decline, 15 km/h). Blood sample (pre, post, 4 h) analyses included serum concentrations of IL ‐1β, IL ‐1ra, IL ‐4, IL ‐6, IL ‐8, IL ‐10, matrix metalloprotease‐9 ( MMP ‐9) and creatine kinase ( CK ). Intracellular IL ‐6, IL ‐10, MPO and STAT 3/ SOCS 3 signaling were assessed in mononuclear cells. CK (1573 ± 756 u/L), MMP ‐9 (101 ± 27 ng/mL), neutrophil (9.89 ± 0.76 × 10 9 cells/L) and monocyte counts (1 ± 0.08 × 10 9 cells/L) increased at 4 h. At 4 h serum (7.1 ± 1.3 ng/mL) and monocyte MPO (1.7‐fold) increased, whereas neutrophil MPO decreased (0.8‐fold). Intracellular monocyte IL ‐10 and IL ‐6 decreased by 15% and 20–30%, respectively, coinciding with elevations in serum IL ‐10 of 14.5 ± 4.7 pg/mL and IL ‐6 of 5.4 ± 2.9 pg/mL, suggesting immune cell cytokine release in response to exercise. Intracellular PBMC p‐ STAT 3 to total STAT 3 ratio increased from pre to 4 h. Circulating monocytes are responsive to increased serum IL ‐6 suggesting a negative feedback loop via STAT 3 signaling.