Research Article: Evaluation of the Protective Efficacy of Poly I:C as an Adjuvant for H9N2 Subtype Avian Influenza Inactivated Vaccine and Its Mechanism of Action in Ducks

Date Published: January 30, 2017

Publisher: Public Library of Science

Author(s): Aiguo Zhang, Hanzhang Lai, Jiahua Xu, Wenke Huang, Yufu Liu, Dawei Zhao, Ruiai Chen, Yongchang Cao.


Current commercial H9 avian influenza vaccines cannot provide satisfactory protective immunity against antigenic variant influenza viruses in ducks. Poly I:C, when used as an adjuvant, improves humoral and cellular immunity in many animals but has not been tested in ducks. In this study, we investigated the protective efficacy of Poly I:C as an adjuvant for an inactivated H9N2 Avian influenza vaccine in ducks. We found that an H9N2 vaccine administered with poly I:C (H9-PIC vaccine) induced a significantly more rapid response with higher anti-influenza antibody titers than those of the vaccine alone (H9 vaccine). Moreover, virus shedding was reduced in ducks immunized with the H9-PIC vaccine after challenge with an H9 subtype antigenic variant viruses. IFN-α, IFN-γ, IL-6 and MHC-II mRNA levels were all elevated in ducks receiving the H9-PIC vaccine. In addition, lower expression level of MHC-I may be a reason for inefficient protective ability against heterologous influenza viruses in H9-PIC vaccination of ducks. In conclusion, poly I:C adjuvant enhanced both humoral and cellular immune responses in ducks induced by immunization of inactivated H9N2 vaccine.

Partial Text

Avian influenza viruses (AIV) have a worldwide distribution in a variety of animals including humans, pigs, wild birds and domestic poultry [1, 2]. This group of viruses is responsible for major economic losses to the poultry industry and also responsible for influenza infection in humans [3]. Ducks are the principal natural reservoir for the H9N2 strain of AIV. Interestingly, this antigenic subtype contributed genetic material to the zoonotic H7N9 strain that was responsible for a recent outbreak. Genetic exchange between subtypes plays an important role in AIV dissemination and evolution [1, 2].

Domestic ducks are the natural reservoir of H9N2 that not only leads to huge economic losses in the poultry industry, but also threatens public health. The current H9N2 subtype inactivated vaccine only induces a low protective antibody titer in ducks. It does not effectively eliminate virus shedding in the field [8–12]. When poly I:C was used as adjuvant in previous studies, it enhanced both humoral and cellular immune responses [15, 30, 31]. Its mechanism of action is based upon type I IFN production that enhances dendritic cell maturation and B cell activation. This ultimately leads to induction of potent CD4+ T cell and humoral immune responses [11, 23]. Type I IFN is critical for cross presentation of protein antigens to generate CD8+ T cell responses in mice [13]. However, this type of data is lacking for duck infections, especially concerning the immune responses in immune organs.

This study demonstrated that H9-PIC vaccine more rapidly induced elevated antibody levels and reduced viral shedding against the heterogeneous antigenic variant H9N2 influenza in ducks. Poly I:C adjuvant could significantly improve the efficacy of an inactivated H9 subtype AI vaccine in both humoral and cellular immunity in ducks, suggesting that Poly I:C adjuvant for vaccine could be used to prevent and control H9N2 influenza in ducks.




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