Enhancing effects of immunoactive peptide FR48217 on immunological responses to vaccination by inactivated influenza virus

The adjuvant effect of an immunoactive peptide, FR48217 (FR), was investigated in mice vaccinated with inactivated influenza virus with and without FR (designated as V+FR and V-FR, respectively). Mice were infected with influenza virus A/PR/8/34 28 days after vaccination. The survival rate indicated a strong adjuvant effect of FR on vaccination with inactivated influenza virus. No difference in interferon activity in the pulmonary lavage fluid was found between the V+ FR and V - FR groups. The titres of virus-specific IgA and IgG antibodies in the serum increased after vaccination in both V+ FR and V-FR groups and were significantly higher in the V+ FR group than in the V-FR group. On days 2 and 4 after viral infection, the serum antibody titres decreased sharply and then increased again rapidly. The free IgA and IgG antibody levels in the pulmonary lavage fluid of vaccinated mice started to increase after day 4. It is proposed that one of the mechanisms by which FR has the adjuvant effect on vaccination is the increase of virus-specific IgA and IgG antibodies in the serum, which are diffused into the infection sites of the epithelial tissues in the respiratory tract to neutralize the virus at the early stages of viral infection.