Coexpression of 16.8kDa antigen of Mycobacterium avium paratuberculosis and murine gamma interferon in a bicistronic vector and studies on its potential as DNA vaccine

Paratuberculosis or Johne's disease is a chronic gastric disease of ruminants. For this disease there is no effective treatment or preventive measure available. 16.8kDa protein is an immunogenic protein of Mycobacterium avium paratuberculosis and can be an ideal candidate for developing a DNA vaccine construct. In present study a bicistronic DNA vaccine construct pIR16.8/IFN was developed using eukaryotic vector pIRES 6.1. Two genes MPT (expressing 16.8kDa protein) and murine IFNg were cloned, expressed and immunoreactivity was studied in murine model. Immunoreactivity was also compared with monocistronic construct pIR16.8 expressing 16.8kDa protein. Both pIR16.8 and pIR16.8/IFN showed eukaryotic expression of respective proteins in BHK21 cells. The expressed proteins also showed immunoreactivity when reacted with hyperimmune sera raised against recombinant 16.8kDa protein in western blot assay and immunofluorence assay. Both constructs were used as DNA vaccine in murine model and immunogenecity was studied by DTH, lymphocyte proliferation assay and NO determination. DTH reaction was significantly high in pIR16.8/IFN than pIR16.8 group, similarly lymphocyte proliferation and NO release was higher in pIR16.8/IFN group than pIR16.8 group. This indicated T cell epitopic nature of 16.8kDa protein. The study also showed that co-expression of IFNg with mycobacterial gene can enhance immunogenecity of DNA vaccine and can be used as immunoadjuvant.