Oxidative stress augments toll-like receptor 8 mediated neutrophilic responses in healthy subjects.
BACKGROUND
Excessive oxidative stress has been reported to be generated in inflamed tissues and contribute to the pathogenesis of inflammatory lung diseases, exacerbations of which induced by viral infections are associated with toll-like receptor (TLR) activation. Among these receptors, TLR8 has been reported as a key receptor that recognizes single-strand RNA virus. However, it remains unknown whether TLR8 signaling is potentiated by oxidative stress. The aim of this study is to examine whether oxidative stress modulates TLR8 signaling in vitro.


METHODS
Human peripheral blood neutrophils were obtained from healthy non-smokers and stimulated with TLR 7/8 agonist imidazoquinoline resiquimod (R848) in the presence or absence of hydrogen peroxide (H2O2). Neutrophilic responses including cytokine release, superoxide production and chemotaxis were examined, and the signal transduction was also analyzed.


RESULTS
Activation of TLR8, but not TLR7, augmented IL-8 release. The R848-augmented IL-8 release was significantly potentiated by pretreatment with H2O2 (p < 0.01), and N-acetyl-L-cysteine reversed this potentiation. The combination of H2O2 and R848 significantly potentiated NF-kB phosphorylation and IkBalpha degradation. The H2O2-potentiated IL-8 release was suppressed by MG-132, a proteosome inhibitor, and by dexamethasone. The expressions of TLR8, myeloid differentiation primary response gene 88 (MyD88), and tumor necrosis factor receptor-associated factor 6 (TRAF6) were not affected by H2O2.


CONCLUSIONS
TLR8-mediated neutrophilic responses were markedly potentiated by oxidative stress, and the potentiation was mediated by enhanced NF-kB activation. These results suggest that oxidative stress might potentiate the neutrophilic inflammation during viral infection.
Yanagisawa
Satoru
S
Third Department of Internal Medicine, Wakayama Medical University, School of Medicine, Wakayama, Japan. yngsw@wakayama-med.ac.jp
Koarai
Akira
A
Sugiura
Hisatoshi
H
Ichikawa
Tomohiro
T
Kanda
Masae
M
Tanaka
Rie
R
Akamatsu
Keiichiro
K
Hirano
Tsunahiko
T
Matsunaga
Kazuto
K
Minakata
Yoshiaki
Y
Ichinose
Masakazu
M
D000111:Acetylcysteine / Q000494:pharmacology; D002634:Chemotaxis, Leukocyte / Q000187:drug effects; D016207:Cytokines / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology*; D007249:Inflammation / Q000503:physiopathology* / Q000821:virology; D016209:Interleukin-8 / Q000187:drug effects / Q000378:metabolism; D009504:Neutrophils / Q000502:physiology*; D018384:Oxidative Stress / Q000502:physiology*; D010196:Pancreatic Elastase / Q000097:blood; D010766:Phosphorylation; D012016:Reference Values; D015398:Signal Transduction; D051199:Toll-Like Receptor 7 / Q000819:agonists; D051200:Toll-Like Receptor 8 / Q000819:agonists / Q000502:physiology*; D051996:Transcription Factor RelA / Q000378:metabolism; D014777:Virus Diseases / Q000503:physiopathology
D016207:Cytokines; D007093:Imidazoles; D016209:Interleukin-8; D051199:Toll-Like Receptor 7; D051200:Toll-Like Receptor 8; D051996:Transcription Factor RelA; D006861:Hydrogen Peroxide; D010196:Pancreatic Elastase; C402365:resiquimod; D000111:Acetylcysteine