Evaluation of intramuscular versus intra-dermal inoculation of bacterial plasmid encoding nucleoprotein of influenza virus

The use of bacterial plasmids carrying specific genes of pathogens as genetic vaccines is a relatively new technique for induction of cellular immune responses against microbial pathogens. Mechanisms of production of specific immune responses against these vaccines are not still completely understood. Therefore, it is necessary to examine various routes of inoculation to find the best way of immunization for specific antigens. In this research, intramuscular method of inoculation of influenza vaccine nucleoprotein (NP) encoding vector was compared with that of intra-dermal method. In this study, the ability of two different methods of immunization (intramuscular and intra-dermal) in induction of CTL responses as well as their efficiency in clearance of influenza virus from the lung of BALB/c mice was compared. Female BALB/c mice were immunized with influenza virus NP expressing plasmids on days 0, 14 and 28. CTL activity of mice was evaluated by lactate dehydrogenase technique two weeks after the last inoculation. In addition, the mice were challenged by live influenza virus and the viral titer was measured 4 days post-challenge in the lungs of animals. The results of experiments demonstrated that intramuscular immunization of mice induces a stronger CTL response. Mice immunized by intramuscular route also showed a higher ability in virus clearance from the lungs. Results of this study showed that different routes of immunization of influenza NP genetic vaccine induce different levels of cell-mediated immune responses and protection from the live virus.