Immune effects against influenza A virus and a novel DNA vaccine with co-expression of haemagglutinin- and neuraminidase-encoding genes

Abstract

The high variability of influenza virus causes difficulties in the control and prevention of influenza, thus seeking a promising approach for dealing with these problems is a hot topic. Haemagglutinin (HA) and neuraminidase (NA) are major surface antigens of the influenza virus, and provide effective protection against lethal challenges with this virus. We constructed a DNA vaccine (pHA-IRES2-NA) that co-expressed both HA and NA, and compared its protective efficacy and immunogenic ability with that of singly expressed HA or NA, or a mixture of the two singly expressed proteins. Our findings showed that both HA and NA proteins expressed by pHA-IRES2-NA could be detected in vivo and in vitro. The protection of DNA vaccines was evaluated by serum antibody titres, residual lung virus titres and survival rates of the mice. In the murine model, immunization of pHA-IRES2-NA generated significant anti-HA and anti-NA antibody, increased the percentage of CD8+ cells and gamma interferon-producing CD8+ cells and the ratio of Th1/Th2 (T helper) cells, which was comparable to the effects of immunization with HA or NA DNA alone or with a mixture of HA and NA DNA. All the mice inoculated by pHA-IRES2-NA resisted the lethal challenge by homologous influenza virus and survived with low lung virus titre. In addition, previous studies reported that co-expression allowed higher-frequency transduction compared to co-transduction of separated vector systems encoding different genes. The novel HA and NA co-expression DNA vaccine is a successful alternative to using a mixture of purified HA and NA proteins or HA and NA DNA.