4.5 Article

Adjuvant activity of PCP-II, a polysaccharide from Poria cocos, on a whole killed rabies vaccine

Journal

VIRUS RESEARCH
Volume 270, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.virusres.2019.06.001

Keywords

Rabies vaccine; Adjuvant; Cellular immunity; Polysaccharide; Antibody titer

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Funding

  1. National Key Research and Development Program of China [2016YFD0501004]
  2. National Natural Science Foundation of China [31402175]
  3. Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses (Yangzhou, People's Republic of China)

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Adjuvants are important components of vaccination strategies because they boost and accelerate the immune response. The aim of this study was to investigate the adjuvant activity of PCP-II, a polysaccharide isolated from Poria cocos, together with an inactivated rabies vaccine. The polysaccharide PCP-II was compared with the common veterinary rabies vaccine adjuvant Alhydrogel by co-administration of either adjuvant with the inactivated rabies virus rCVS-11-G to mice via the intramuscular route. Blood samples were collected to determine the virus-neutralizing antibody (VNA) titer and assess activation of B and T lymphocytes. Inguinal lymph node samples were collected, and proliferation of B lymphocytes was measured. Splenocytes were isolated, and antigen-specific cellular immune responses were evaluated by enzyme-linked immunospot and immunosorbent assays (ELISpot assay and ELISA, respectively). The results showed that PCP-II enhanced and promoted an increase in the VNA titer in the mice compared to Alhydrogel. Flow cytometry assays revealed that the polysaccharide activated more B lymphocytes in the lymph nodes and more B and T lymphocytes in the blood. Assessment of antigen-specific cellular immune responses showed that PCP-II strongly induced T lymphocyte proliferation in the spleen and high levels of cytokine secretion from splenocytes. All of these data suggest that PCP-II possesses excellent adjuvant activity and enhances both cellular and humoral immunity in mice. After examining the adjuvant activities of PCP-II in mice, dogs were immunized with rCVS-11-G together with Alhydrogel or PCP-II as an adjuvant; the control group was injected with a commercial rabies vaccine. Serum samples were collected, and the VNA titers were measured. PCP-II caused increases in the VNA titers in both the booster and single-dose immunization tests when co-administered with rCVS-11-G compared with Alhydrogel. The VNA titer of the commercial vaccine group was also significantly lower than that of the PCP-II group. These data indicate that PCP-II is an excellent candidate adjuvant for inactive rabies vaccines in the veterinary setting.

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