Evaluation of aqueous extracts of Cistanche deserticola as a polysaccharide adjuvant for seasonal influenza vaccine in young adult mice

Abstract

Adjuvants can improve the efficacy of influenza vaccines and are still a hot spot in the study and development of influenza vaccines. In this report, the effects of aqueous extracts of Cistanche deserticola (AECD) as a polysaccharide adjuvant on seasonal influenza vaccines (IVV) were explored. The experimental data of anti-IVV IgG₁ and IgG as well as hemagglutinin inhibition (HI) titers in young adult mice indicated that IVV intramuscularly co-injected with AECD was significantly more immunogenic than alum-adjuvanted or non-adjuvanted IVV. AECD-adjuvanted vaccine could rapidly initiate specific IgG response. Similarly, IVV with AECD augmented significantly lymphocyte proliferation and increased the positive rates of CD4⁺, CD8⁺ and CD44⁺ T cells from draining lymph nodes and spleens. Importantly, IVV with AECD could induce the Th1 immune response, as indicated by higher IgG_2a levels accompanied by the induction of IFN-γ in CD4⁺ and CD8⁺ T cells. Additionally, IVV with AECD activated dendritic cells (DCs) and decreased the expression of Treg cells. There were no noticeable side effects after the vaccination. In brief, the addition of AECD enhanced immunogenicity to seasonal influenza vaccine by the induction of HI antibody generation, more rapid humoral immune responses, and a balanced Th1-/Th2-type response, effective T-cell responses, which may be important for seasonal influenza vaccines with broad and long lasting immunity.

Keywords: Aqueous extract; Cistanche deserticola; Influenza vaccine; Polysaccharide adjuvant; Th1/Th2 response.