title: Neutrophil Depletion Attenuates Muscle Injury after Exhaustive Exercise.
abstract: The infiltration of macrophages in skeletal muscle during exhaustive exercise promotes inflammation, myofiber lesion, and muscle injury. Although neutrophils upregulate macrophage infiltration in skeletal muscles during exercise, the role of neutrophils in promoting muscle injury after exhaustive exercise remains unclear. In this study, we investigated the effects of preexercise neutrophil depletion with antineutrophil antibody treatment on muscle injury, inflammation, and macrophage infiltration after exhaustive exercise.
  
  
  
  Male C57BL/6J mice were randomly assigned to four groups, namely, sedentary with control antibody (n = 10), sedentary with antineutrophil antibody (n = 10), exhaustive exercise with control antibody (n = 10), and exhaustive exercise with antineutrophil antibody (n = 10). The mice were given intraperitoneal injection of the antineutrophil antibody (anti-Ly-6G, clone 1A8) or the control antibody (anti-Ly-6G, clone 2A3), and remained inactive or performed exhaustive exercise on a treadmill 48 h after the injection. Twenty-four hours after the exhaustive exercise, the gastrocnemius muscles were removed for histological and polymerase chain reaction (PCR) analyses. Infiltration of neutrophils and macrophages was evaluated with Ly-6G and F4/80 immunohistochemistry staining procedures. Muscle fiber injury was detected based on the number of IgG staining fiber. The mRNA expression levels of proinflammatory cytokines and chemokines were evaluated with real-time reverse transcription PCR.
  
  
  
  Exhaustive exercise increased neutrophil infiltration into the gastrocnemius muscle substantially by 3.1-fold and caused muscle injury, but these effects were markedly suppressed by preexercise treatment with antineutrophil antibody (neutrophil infiltration, 0.42-fold, and muscle injury, 0.18-fold). Treatment with antineutrophil antibody also decreased macrophage infiltration (0.44-fold) and mRNA expression of tumor necrosis factor-α (0.55-fold) and interleukin-6 (0.51-fold) in the skeletal muscle after exhaustive exercise.
  
  
  
  These results suggest that neutrophils contribute to exacerbating muscle injury by regulating inflammation through the induction of macrophage infiltration.
authors.affiliation: 1Institute for Nanoscience and Nanotechnology, Waseda University, Tokyo, JAPAN; 2Research Fellow of the Japan Society for the Promotion of Sciences, Tokyo, JAPAN; 3School of Health and Sports Science, Juntendo University, Chiba, JAPAN; 4Graduate School of Sport Sciences, Waseda University, Tokorozawa, Saitama, JAPAN; and 5Faculty of Sport Sciences, Waseda University, Tokorozawa, Saitama, JAPAN.
authors.forename: Noriaki
authors.initials: N
authors.lastname: Kawanishi
authors.forename: Tsubasa
authors.initials: T
authors.lastname: Mizokami
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Niihara
authors.forename: Koichi
authors.initials: K
authors.lastname: Yada
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Suzuki
mesh_terms: D000818:Animals; D007249:Inflammation / Q000503:physiopathology; D015850:Interleukin-6 / Q000378:metabolism; D008264:Macrophages / Q000502:physiology*; D008297:Male; D008810:Mice, Inbred C57BL; D018482:Muscle, Skeletal / Q000293:injuries* / Q000378:metabolism / Q000502:physiology; D009504:Neutrophils / Q000502:physiology*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D011897:Random Allocation; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D015850:Interleukin-6; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha