Evaluation of Chinese Yam Polysaccharide-Aluminum Hydroxide Nanoparticle Combination Adjuvant for Porcine Circovirus Type 2 Vaccine and Underlying Mechanisms

Conventional alum adjuvants primarily induce a Th2 humoral immune response yet fail to provoke a Th1 cellular immune response. In our preceding study, we constructed a novel and biosafe nanoparticle-based adjuvant system, in which the Chinese yam polysaccharide (CYP), as the immunopotentiator, was loaded onto aluminum hydroxide nanoparticles (CYP-AlNPs). Herein, we further investigated the adjuvant activity of the CYP-AlNPs against the porcine circovirus type 2 (PCV2) vaccine. Moreover, we further explored the underlying molecular mechanisms by which the CYP-AlNPs stimulated the dendritic cell (DC) activation. Our results demonstrated that the CYP-AlNPs exhibited good adjuvant activity as an adjuvant to the PCV2 vaccine, which elicited a robust antibody response, facilitated the generation of the germinal center in lymph nodes, increased the population of CD4+ and CD8+T cells, and enhanced the production of IFN-γ and IL-6, thereby inducing a mixed Th1 and Th2 immune response. Notably, our results revealed the crucial role of the NLRP3 inflammasome and TLR4-NF-κB signaling pathways in DC activation stimulated by the CYP-AlNPs. The present study highlighted the potential of polysaccharide-alum nanoparticle combination adjuvants that act through different mechanisms to achieve enhanced immune responses, providing a new perspective on vaccine design.