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Open Access Research

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

Jun Dai1, Decui Pei1, Baoning Wang1, Yu Kuang1, Laifeng Ren1, Kang Cao1, Bin Zuo1, Jingjing Shao1, Sha Li1, Zhonghua Jiang1, Hong Li2 and Mingyuan Li13*

Author Affiliations

1 Department of Microbiology, West China School of Preclinical and Forensic Medicine, Sichuan University, Chengdu, Sichuan 610041, PR China

2 Key Laboratory of Obstetric & Pediatic Disease and Birth Defects of Ministry of Education, West China Second University Hospital, Sichuan University, Chengdu, Sichuan, 610041, China

3 State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, Sichuan 610041, PR China

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Virology Journal 2013, 10:40  doi:10.1186/1743-422X-10-40

Published: 31 January 2013

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.

Keywords:
Staphylococcus aureus; Influenza a viruse; Mycobacterium tuberculosis secreted antigen Ag85A; DNA vaccine