Cultivated Artemisia rupestris L. polysaccharide CARP2 as an adjuvant for influenza vaccines to prolong immune responses

In the study, the adjuvant features of the immunoregulatory polysaccharide component CARP2 isolated from cultivated Artemisia rupestris L. for influenza virus vaccine (IVV) and the mechanism responsible for its action in DCs were further explored. CARP2 showed a typical absorbance peak of polysaccharides in spectral analysis. At two doses of CARP2-adjuvanted IVV, IgG, hemagglutination inhibition (HI) titers, and effector/memory T cells were generated and lasted for 275 days without adverse events. CARP2 primed rapid HI and IgG, IgG2a/IgG1 ratio, splenocyte proliferation, and cytotoxic T lymphocyte (CTL), and facilitated the generation of INF-γ and IL-4 by activating DCs and regulatory T cells (Tregs). Additionally, CARP2 achieved the ten-fold dose-sparing effect. In vitro, CARP2 stimulated DCs to prime the production of Th1/Th2 cytokines and CCR7 and activated MyD88-dependent pathway by upregulating the expressions of TLR4, MyD88, TRAF-6, and p65. In contrast, MyD88, TRAF-6, and NF-κB inhibitors partially blocked the effect through reducing related cytokines and proteins. Overall, CARP2 promoted IVV efficacy, which was involved in the modulation of Th1/Th2 responses and shifted toward Th1-polarizing response via TLR4/MyD88/TRAF/NF-κB activation in DCs.