Administration of mBD4 reduced A (H1N1)09virus replication in obese mice respiratory tract

Abstract

Background: Mouse beta-Defesin 4 (mBD4) is mainly expressed by epithelial cells and is thought to be the first line of defense. A(H1N1)09 pandemic influenza virus caused severe respiratory tract infection and led more death in obese population. The mBD4 should play important roles but its expression and function in response to influenza virus infection has not been fully elaborated. Methods: The expression of mBD4 in mouse lung epithelial cell line LA4 and C57 BL/6 mouse respiratory tissues following influenza virus infection were studied by quantitative real-time polymerase chain reaction (PCR) and also by immunofluorescence or immunohistochemistry staining. Viral replication in mouse respiratory tissues were studied by plaque assay. Virus induced cytokines (TNF-α and IL-6) responses were studied by ELISA. Results: Firstly, we showed that after inoculation with 10 multiplicity of infection (MOI) A(H1N1)09 virus or H7N9(AH1) virus, mBD4 was significantly induced on mRNA level at an early stage. Immunofluorescence staining showed there was higher mBD4 expression in H7N9(AH1) virus–infected LA4 cells at 24 hours post infection. Higher mBD4 induction resulted in lower viral load in LA4 cell lysates when comparing H7N9(AH1) virus–infected cells to A(H1N1)09 virus–infected cells. The expression of mBD4 in mouse respiratory tissue was studied and compared between lean and obese mice. Quantitative real-time PCR showed significantly higher basal level of mBD4 in obese mice’s lung tissues but not in trachea tissues compared with lean mice. Immunohistochemical staining of formalin-fixed mice lung tissues showed there was stronger expression of mBD4 in epithelial cells lining bronchioles in obese mice which indicated a higher basal expression of mBD4 in obese mice lung tissues. Upon infection with A(H1N1)09 influenza virus, a quick induction of mBD4 in lean mice trachea tissue were observed at 12 hours p.i. while there was no induction of mBD4 in obese mice trachea tissues even at day 4 p.i.. For the lung tissues, induction of mBD4 was observed in lean mice following A(H1N1)09 infection at day 4 p.i., but a dramatic decrease in mBD4 was observed in obese mice lung tissues. Accordingly we also observed a lower viral load and cytokine levels in lean mice. After giving the recombinant mBD4 protein(6mg/kg) after infection of A(H1N1)09 in obese mice, we observed a reduced viral load in respiratory tissues. Conclusion: Influenza virus infection could induce the expression of mBD4 in vitro and in vivo. Lean and obese mice showed different pattern of change in mBD4 induction after A(H1N1)09 influenza virus infection. The treatment of H1N1 infection in obese mice with recombinant mBD4 could reduce viral load in respiratory tract which indicated mBD4 may play important roles in this infection.