A Nanovaccine Based on Cationic <i>Lentinan</i> Adjuvant Enhances Protective Immunity against H1N1 and H9N2 Influenza Virus Infection

Influenza viruses are highly prevalent and continuously evolving respiratory pathogens that pose a significant threat to global public health and the poultry industry. Immunization remains the primary approach to preventing infection and reducing the risk of an influenza pandemic. Nanoparticles not only serve as delivery vehicles for antigens but also enhance antigen-specific immune responses. Polysaccharide nanoparticles not only amplify the immunostimulatory capacity of polysaccharides but also exhibit superior adjuvant effects. In this study, we investigated the effect of cationic <i>Lentinan</i> (CLNT) as an adjuvant for influenza vaccines. CLNT significantly enhanced the production of specific antibodies against influenza antigens (H1N1 and H9N2) and promoted a strong humoral immune response. Compared with the control group, the CLNT group showed 8.49- and 5.23-fold increases in H1N1- and H9N2-specific IgG antibody levels, respectively. CLNT also activated dendritic cells, T cells, and B cells, thus triggering the cellular immune response. In addition, CLNT effectively inhibited the replication of H1N1 and H9N2 viruses in the trachea and lungs, indicating its potent protective immune effect against influenza virus challenge. This study suggests that CLNT enhances both the potency and breadth of immune responses against influenza viruses, presenting it as a promising adjuvant and offering new options for designing next-generation influenza vaccines.