Evaluation and characteristics of immunological adjuvant activity of purified fraction of <i>Albizia julibrissin</i> saponins

Purpose: The purified fraction of Albizia julibrissin saponins (AJSAF) was evaluated and characterized for the adjuvant activity on porcine reproductive and respiratory syndrome virus (PRRSV) vaccine. Methods: The effects of AJSAF on serum PRRSV N protein-specific antibody titers, splenocyte proliferation, natural killer (NK) cell activity, mRNA expression of cytokines and transcription factors, secretion of cytokines, T cells response in splenocytes, as well as delayed type hypersensitivity (DTH) in the mice immunized PRRSV vaccine were determined by ELISA, MTT assay, flow cytometry and quantitative real-time PCR (qRT-PCR). Results: AJSAF not only significantly enhanced the serum PRRSV N protein-specific IgG, IgG1, IgG2a and IgG2b antibody titers in the mice immunized with PRRSV CH-1R modified live vaccine (CH-1R MLV), inactivated vaccine (CH-1R IAV), and highly pathogenic JXA1-R modified live vaccine (JXA1-R MLV), but promoted the concanavalin A (Con A)-, lipopolysaccharide (LPS)- and PRRSV N protein-stimulated splenocyte proliferation, the activities of NK cells and delayed type hypersensitivity (DTH) in the mice immunized CH-1R MLV. AJSAF also remarkably induced the production of both Th1 (IFN-γ) and Th2 (IL-10) cytokines, and up-regulated the mRNA expression levels of Th1 cytokines (IFN-γ and IL-2) and transcription factors (T-bet and STAT4) as well as Th2 cytokines (IL-4 and IL-10) and transcription factors (GATA-3 and STAT6) in splenocytes from the CH-1R MLV-immunized mice. Furthermore, AJSAF markedly increased the frequencies of PRRSV N protein-specific Th1 (INF-γ+ and IL-2+) and Th2 (IL-4+ and IL-10+) CD4 T cells as well as Tc1 (INF-γ+ and IL-2+) and Tc2 (IL-4+ and IL-10+) CD8 T cells in splenocytes from the CH-1R MLV-immunized mice. Conclusions: Our results demonstrated that AJSAF had a potential to enhance and improve immune responses and elicit both Th1/Th2 and Tc1/Tc2 response to PRRSV vaccine, and that AJSAF would be a promising adjuvant candidate for PRRSV vaccine.