Adjuvant Efficacy Of Lycium Barbarum Polysaccharides For Intranasally Administered Split Pandemic (H1N1) 2009 Influenza Vaccine

Influenza virus is one of the major pathogens threatening human health. In the end of April 2009, a novel influenza H1N1 (A/California/7/2009) outbroke in Mexico, and then spread rapidly to more than one hundred countries. On June 11,2009, the World Health Organization (WHO) officially declared to raise the status from epidemic to worldwide pandemic alert, highest level phase 6, which meant that the first global influenza pandemic of the new millennium had begun. This novel, swine (H1N1) influenza A virus was formed through reassortment from several kinds of influenza virus strains, against which humans were unable to induce immune response. It was more likely to infect younger people than older people, and what’s worse, the virus would transmit to others within two or three days. The surveillance and prevention of influenza is a long-term and arduous task with continuously updating challenges. The research on influenza virus and the development of influenza vaccine has great significance to public health.Vaccination is the best method to prevent influenza virus. The traditional vaccines are vaccinated via intramuscular route, whereas the influenza virus infects through upper respiratory tract, invading into animals and humans through the respiratory mucosa. Thus mucosal immunity against infection is particularly important in prevention of influenza virus. Intranasal administration of influenza vaccine by drips or spray into nostril can induce a strong local mucosal immune response, secreting specific slgA, which can not only prevent the infection effectively in time, but also provide better cross-protection than the IgG in serum.The antigenicity of vaccine can be enhanced and the immune response may be optimized by an adjuvant, resulting in the decrease of antigen dose. For this reason, safe and effective mucosal adjuvant for inactivated influenza virus vaccine will be favorable to the protection of organism. Lycium barbarum polysaccharides (LBP) is a kind of heteropolysaccharide consisting of six monosaccharide, which is extracted from the Lycium barbarum fruit. Many researches have proved that LBP has remarkable immunopotentiation, such as promoting the proliferation of lymphocytes, regulating the secretion of cytokines and nhancing the specific antibody and CTL responses.In the present study, female BALB/c mice were immunized intranasally with different amounts of monovalent pandemic H1N1 influenza split vaccine, with or without LBP as an adjuvant. Mice vaccinated only with LBP and unimmunized were set as control groups. The effect of LBP as a mucosal adjuvant to the intranasally administered split pandemic H1N1 vaccine would be explored. The IgG, IgG1 and IgG2a antibody titers in serum and IgA antibody titers in mouse nasal washes were determined by ELISA method, and hemagglutination inhibiting antibody titers in serum were detected by HI assay. The induction of cellular immunity was evaluated in detection of IFN-y secretion by the Elispot method. Two weeks after the secondary immunization the mice were challenged with a lethal dose of homologous influenza virus. The protective ability provided by vaccination was evaluated by detection of residue virus titers in lung, body weight change and survival rates of mice.The experimental results showed that, specific IgG antibody titers in sera of mice increased as the amount of vaccine increased. When LBP was added, higher IgG antibodies were induced at the same vaccine dosage, showing that LBP has an effect in enhancing humoral immunity. As for IgG subclasses, IgGl antibodies were a little bit higher than IgG2a in all groups, and LBP adjuvanted vaccine could induce higher subtype antibodies than vaccine-alone. It indicated that split inactivated vaccine induced a mixed Thl/Th2 response, and LBP as an adjuvant didn’t change the type of immune response induced by the vaccine. Specific IgA antibodies were detected in nasal washes of higher dose vaccine groups, indicating that local mucosal immunity was induced. HI assay showed that the vaccine mixed with LBP induced higher levels of hemagglutination inhibiting antibody than the vaccine alone. Secretion of IFN-γ in spleen cells of mice vaccinated with high dose of vaccine with LBP was significantly higher than in other groups, indicating that strong cellular immune responses were induced. Protective abilities against the lethal dose of homologous virus were positively correlated with the dose of vaccine, and LBP showed excellent adjuvant effect Based on these results, we could draw a conclusion that LBP is a promising adjuvant that can strengthen the immune responses induced by intranally administered split influenza vaccine.