Bovine neutrophils stimulated with Streptococcus uberis induce neutrophil extracellular traps, and cause cytotoxicity and transcriptional upregulation of inflammatory cytokine genes in bovine mammary epithelial cells

Characteristics of neutrophil chemotaxis in bottlenose dolphin (Tursiops truncatus)

Cetaceans have adapted to aquatic life by evolving various anatomic and physiologic traits, but biological defense mechanisms specific to aquatic mammals that protect against pathogenic microorganisms in the aquatic environment have not been elucidated. In this study, we investigated the migration of polymorphonuclear leukocytes in bottlenose dolphins in response to various chemotactic factors and compared the migration response with that of terrestrial animals such as cows and humans to characterize biological defense mechanisms unique to cetaceans. Bottlenose dolphin neutrophils showed strong chemotactic activity toward zymosan-activated serum and recombinant human interleukin-8 but no chemotaxis toward N-formyl-methionyl-leucyl-phenylalanine or leukotriene B4 at any concentration examined. Bovine and human neutrophils showed the strongest chemotactic activity at 37°C, whereas chemotactic activity declined significantly at 15°C and 4°C. By contrast, bottlenose dolphin neutrophils exhibited relatively strong chemotactic activity even at 15°C. These results suggest that the mechanism by which bottlenose dolphin neutrophils detect chemoattractants differs from that of terrestrial mammals and that the immune system of cetaceans may be cold-adaptive, allowing the animals to exert robust host defense responses in aquatic habitats, which tend to be colder than the terrestrial environment.

Antioxidative Sirt1 and the Keap1-Nrf2 Signaling Pathway Impair Inflammation and Positively Regulate Autophagy in Murine Mammary Epithelial Cells or Mammary Glands Infected with Streptococcus uberis

Streptococcus uberis mastitis in cattle infects mammary epithelial cells. Although oxidative responses often remove intracellular microbes, S. uberis survives, but the mechanisms are not well understood. Herein, we aimed to elucidate antioxidative mechanisms during pathogenesis of S. uberis after isolation from clinical bovine mastitis milk samples. S. uberis's in vitro pathomorphology, oxidative stress biological activities, transcription of antioxidative factors, inflammatory response cytokines, autophagosome and autophagy functions were evaluated, and in vivo S. uberis was injected into the fourth mammary gland nipple of each mouse to assess the infectiousness of S. uberis potential molecular mechanisms. The results showed that infection with S. uberis induced early oxidative stress and increased reactive oxygen species (ROS). However, over time, ROS concentrations decreased due to increased antioxidative activity, including total superoxide dismutase (T-SOD) and malondialdehyde (MDA) enzymes, plus transcription of antioxidative factors (Sirt1, Keap1, Nrf2, HO-1). Treatment with a ROS scavenger (N-acetyl cysteine, NAC) before infection with S. uberis reduced antioxidative responses and the inflammatory response, including the cytokines IL-6 and TNF-α, and the formation of the Atg5-LC3II/LC3I autophagosome. Synthesis of antioxidants determined autophagy functions, with Sirt1/Nrf2 activating autophagy in the presence of S. uberis. This study demonstrated the evasive mechanisms of S. uberis in mastitis, including suppressing inflammatory and ROS defenses by stimulating antioxidative pathways.