A novel DNA vaccine expressing the Ag85A-HA2 fusion protein provides protection against influenza A virus and Staphylococcus aureus

Jun Dai,Sha Li,Laifeng Ren,Bin Zuo,Decui Pei,Mingyuan Li,Yu Kuang,Zhonghua Jiang,Baoning Wang,Hong Li,Jingjing Shao,Kang Cao

doi:10.1186/1743-422x-10-40

Abstract

Secondary pneumonia due to Staphylococcus aureus (S. aureus) causes significant morbidity and mortality. The aim of the research was designed a novel DNA vaccine encoding the Mycobacterium tuberculosis secreted antigen Ag85A fused with the influenza A virus (IAV) HA2 protein to provide protection against both influenza and secondary infection with S. aureus. The DNA vaccine vector efficiently expressed the encoded antigen in mammalian cells, as determined by RT-PCR, Western blotting and immunofluorescence analysis. Mice were immunized with the vaccine by intramuscular injection before challenge with IAV and S. aureus. The pulmonary and the splenocyte culture IFN-γ levels were significant higher in immunized mice than their respective controls. Although the antibody titer in the HI test was low, the sera of mice immunized with the novel vaccine vector were effective in neutralisation assay in vitro. The vaccine could reduce the loss of body weight in mice during IAV challenge. Both Western blotting and RT-PCR showed that the vaccine markedly enhanced toll like receptor 2 (TLR2) expression in splenocytes after the secondary infection with S. aureus. The survival rate of mice with high TLR2 expression (pEGFP/Ag85A-HA2 or iPR) was significantly increased compared with mice immunized with pEGFP/HA2 after challenge with S. aureus. However, the pulmonary IL-10 concentration and S. aureus titer were significantly decreased in immunized mice, and expression of TLR2 was increased after challenge with S. aureus. These results demonstrated that Ag85A could strengthen the immune response to IAV and S. aureus, and TLR2 was involved in the host response to S. aureus.

Highlights

Secondary pneumonia due to Staphylococcus aureus (S. aureus) is a significant cause of mortality associated with influenza A virus (IAV) infection [1,2]
As it is possible that Ag85A can upregulate toll-like receptor 2 (TLR2) expression and immune activation has been shown to offer protection against S. aureus, we hypothesized that immune reactions to Ag85A may be able to eliminate this bacteria [10,11]
The upregulation of TLR2 may be helpful against bacterial infection, it has been suggested that TLR2 does not contribute to host responses during post-influenza pneumonia [12], it is not yet clear whether upregulation of TLR2 would be beneficial in such a scenario

Summary

Introduction

Secondary pneumonia due to Staphylococcus aureus (S. aureus) is a significant cause of mortality associated with influenza A virus (IAV) infection [1,2]. To enhance immune responses against both IAV and S. aureus infections. The Bacille Calmette-Guérin (BCG) vaccine against Mycobacterium tuberculosis has been shown to have a marked immunomodulatory effect in combination with influenza vaccines and can enhance antigen-specific antibody production. The Th1 cytokine, interferon (IFN)-γ, can upregulate expression of toll-like receptor 2 (TLR2), which recognizes Staphylococcal peptidoglycans and induces activation of immune responses [9]. As it is possible that Ag85A can upregulate TLR2 expression and immune activation has been shown to offer protection against S. aureus, we hypothesized that immune reactions to Ag85A may be able to eliminate this bacteria [10,11]. The upregulation of TLR2 may be helpful against bacterial infection, it has been suggested that TLR2 does not contribute to host responses during post-influenza pneumonia [12], it is not yet clear whether upregulation of TLR2 would be beneficial in such a scenario

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