Dampness Can Promote the Influenza A Virus and Worsen Its Prognosis by Upregulating the TLR7 Signaling Pathway.

Context • Outbreaks of the influenza A virus (IAV) are increasingly recognized as a global public health issue, affecting a large proportion of the world's population. A number of studies have provided epidemiologic evidence that dampness and mold are consistently associated with multiple allergic and respiratory effects, but they focused on dampness-related pathogenic microorganisms leading to allergy rather than the dampness itself. Objective • The current study intended to examine the effects of a damp environment on the promotion of the IAV and determine the adverse effects on its prognosis through upregulation of the toll-like receptor 7 (TLR7)-signaling pathway in the lung. Design • The research team performed an animal study. Setting • The study was performed at Jinan University (Guangzhou, China). Animals • A total of 144 specific-pathogen-free, C57BL/6j mice were included in the study, divided into 6 groups with 24 mice in each group. Intervention • The mice were randomly divided into the 6 groups, with 24 mice in each group: (1) group A: normal mice, a control group; (2) group B: normal mice living in a damp environment, a second control group; (3) group C: virally infected mice living in a normal environment; (4) group D: virally infected mice living in a damp environment; (5) group E: virally infected mice living in a normal environment and receiving treatment with 0.2 mL/d of 0.78 mg/mL oseltamivir; and (6) group F: virally infected mice living in a damp environment and receiving treatment with 0.2 mL/d of 0.78 mg/mL oseltamivir. Outcome Measures • Real-time quantitative polymerase chain reaction was used to measure the mRNA expression of TLR7, myeloid differentiation primary response gene 88 (MyD88), tumor necrosis factor receptor associated factor 6 (TRAF6), interleukin 1 receptor-associated kinase 4 (IRAK4), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in the TLR7 signaling pathway and the viral replication level in the lung. Results • The mice began to lose weight after being infected with IAV, especially those mice in groups D and F, where the mice were lost weight more quickly than those in groups C and E. The damages in group F were more serious than for mice in group E. In groups C and D, the mRNA TLR7, MyD88, TRAF6, IRAK4, and NF-κB were upregulated after viral infection (P < .01). After the IAV infection, the expression of TLR7, MyD88, TRAF6, and NF-κB mRNA in group D was higher (P < .01) than in group C. The oseltamivir treatment reduced the mRNA expression in the TLR7 signaling pathways (P < .01), both in the damp environment and normal environment. The expression of mRNA in the TLR7 signaling pathways was lower in group F than in group E (P < .01). Conclusions • The study suggests that dampness can promote the IAV infection and worsen its prognosis by upregulating the TLR7 signaling pathway.