Adjuvant effects mediated by the carbohydrate recognition domain of Agrocybe aegerita lectin interacting with avian influenza HN viral surface glycosylated proteins.

Objective: To evaluate the potential adjuvant effect of Agrocybe aegerita lectin (AAL), which was isolated from mushroom, against a virulent HN strain in vivo and in vitro.

Methods: In trial 1, 50 BALB/c male mice (8 weeks old) were divided into five groups (n=10 each group) which received a subcutaneous injection of inactivated HN (control), inactivated HN+0.2% (w/w) alum, inactivated HN+0.5 mg recombinant AAL/kg body weight (BW), inactivated HN+1.0 mg AAL/kg BW, and inactivated HN+2.5 mg AAL/kg BW, respectively, four times at 7-d intervals. In trial 2, 30 BALB/c male mice (8 weeks old) were divided into three groups (n=10 each group) which received a subcutaneous injection of inactivated HN (control), inactivated HN+2.5 mg recombinant wild-type AAL (AAL-wt)/kg BW, and inactivated HN+2.5 mg carbohydrate recognition domain (CRD) mutant AAL (AAL-mutR63H)/kg BW, respectively, four times at 7-d intervals. Seven days after the final immunization, serum samples were collected from each group for analysis. Hemagglutination assay, immunogold electron microscope, lectin blotting, and co-immunoprecipitation were used to study the interaction between AAL and HN in vitro.

Results: IgG, IgG1, and IgG2a antibody levels were significantly increased in the sera of mice co-immunized with inactivated HN and AAL when compared to mice immunized with inactivated HN alone. No significant increase of the IgG antibody level was detected in the sera of the mice co-immunized with inactivated HN and AAL-mutR63H. Moreover, AAL-wt, but not mutant AAL-mutR63H, adhered to the surface of HN virus. The interaction between AAL and the HN virus was further demonstrated to be associated with the CRD of AAL binding to the surface glycosylated proteins, hemagglutinin and neuraminidase.

Conclusions: Our findings indicated that AAL could be a safe and effective adjuvant capable of boosting humoral immunity against HN viruses in mice through its interaction with the viral surface glycosylated proteins, hemagglutinin and neuraminidase.