Pacific oyster-derived polysaccharides enhance antigen-specific T helper (Th)1 immunity in vitro and in vivo

Bacterial and fungal polysaccharides are well known as being immunoactive. However, evidence pertaining to the immunomodulatory activity of polysaccharides derived from animal origins is scarce. This study investigated the effects of an extract of oyster (Crassostrea gigas) polysaccharides (OPS) on antigen-specific T-cell immunity. For in vitro studies, ovalbumin (OVA)-primed splenocytes were exposed to OPS and re-stimulated with OVA in culture to induce antigen-specific responses. For in vivo studies, mice were administered with OPS prior to OVA sensitization, and the functionality of their splenocytes was examined. Direct exposure of OVA-primed splenocytes to OPS (10-500 μg/mL) resulted in a marked enhancement of the cell metabolic activity and proliferation. Exposure to OPS also augmented the expression of the T helper (Th)1 cytokine interferon (IFN)-γ, whereas the Th2 cytokine interleukin-4 was suppressed. The enhancement of antigen-specific IFN-γ expression was further demonstrated in splenocytes of mice administered with OPS (100 and 200 mg/kg). Moreover, OPS enhanced the mRNA expression of T-bet, a transcription factor governing the development of Th1 cells, by splenocytes. Taken together, these results demonstrated that OPS modulated antigen-specific T cell responses, including antigen-induced splenocyte proliferation and T-cell cytokine expression. In addition, OPS polarized the Th1/Th2 immunobalance toward the Th1-dominant direction, which may be attributed to the up-regulation of Th1 cell development.