Extraction, preliminary characterization and immunostimulatory activity in vitro of a polysaccharide isolated from Strongylocentrotus nudus eggs

A new water-soluble polysaccharide (SEP-2), with a molecular weight of 6.78 × 105 Da, was isolated from Strongylocentrotus nudus eggs under the extraction conditions optimized by response surface methodology (RSM). Preliminary characterization of SEP-2 was performed by HPSEC and GC–MS, indicating that SEP-2 could be a d-glucan containing a (1 → 4)-linked d-Glcp backbone with (1 → 3)-linked d-Glcp side chains. In subsequent immunostimulatory studies, significantly enhanced ROS level, NO production and inflammatory cytokines secretion (IL-1β, IL-6, and TNF-α) were observed in SEP-2 treated murine macrophage cell line RAW264.7. These results suggest that SEP-2 might have the capability to enhance the microbicidal activity and killing function of macrophages through the polarization toward the pro-inflammatory M1 state.