EPSAH, an exopolysaccharide from Aphanothece halophytica GR02, improves both cellular and humoral immunity as a novel polysaccharide adjuvant

EPSAH is an exopolysaccharide from Aphanothece halophytica GR02. The present study was designed to evaluate its toxicity and adjuvant potential in the specific cellular and humoral immune responses in ovalbumin (OVA) in mice. EPSAH did not cause any mortality and side effects when the mice were administered subcutaneously twice at the dose of 50 mg·kg−1. Hemolytic activity in vitro indicated that EPSAH was non-hemolytic. Splenocyte proliferation in vitro was assayed with different concentrations of EPSAH. The mice were immunized subcutaneously with OVA 0.1 mg alone or with OVA 0.1 mg dissolved in saline containing Alum (0.2 mg) or EPSAH (0.2, 0.4, or 0.8 mg) on Day 1 and 15. Two weeks later, splenocyte proliferation, natural killer (NK) cell activity, production of cytokines IL-2 from splenocytes, and serum OVA-specific antibody titers were measured. Phagocytic activity, production of pro-inflammatory cytokines IL-1 and IL-12 in mice peritoneal macrophages were also determined. EPSAH showed a dose-dependent stimulating effect on mitogen-induced proliferation. The Con A-, LPS-, and OVA-induced splenocyte proliferation and the serum OVA-specific IgG, IgG1, and IgG2a antibody titers in the immunized mice were significantly enhanced. EPSAH also significantly promoted the production of Th1 cytokine IL-2. Besides, EPSAH remarkably increased the killing activities of NK cells from splenocytes in the immunized mice. In addition, EPSAH enhanced phagocytic activity and the generation of pro-inflammatory cytokines IL-1 and IL-12 in macrophages. These results indicated that EPSAH had a strong potential to increase both cellular and humoral immune responses, particularly promoting the development of Th1 polarization.