Evaluation of the Immunostimulatory Effect of Ulvan Polysaccharide on Human Macrophages: Use as a Potential Vaccine Adjuvant

The ulvans are sulfated heteropolysaccharides that can stimulate the immune response in vitro. Using a human cell model, this study aimed to characterize and evaluate the immunostimulatory properties of crude ulvans extracted from <i>Ulva</i> spp., collected in Algarrobo, Chile. The crude ulvans, characterized by spectrophotometric methods, are composed of 47.6% total sugars, 14.3% uronic acids, and 8.9% sulfates, with an average molecular weight of 40.000 kDa. The FTIR spectrum showed bands related to uronic acids, rhamnose, and sulfate groups. GCMS analysis confirmed the presence of rhamnose, xylose, glucose, and galactose, with a predominance of the disaccharides U3s and B3s. HL60 cells differentiated into macrophages were cultured with three concentrations of crude ulvans (25, 50, and 100 μg/mL), with cell viability remaining above 90% at the lower concentrations. The crude ulvan activated CD86 co-stimulatory molecules and promoted the release of IL-6, IL-10, IL-4, and nitric oxide cytokines. The results suggest that ulvan is non-toxic and can activate inflammatory pathways, making it a potential candidate for studies as a vaccine adjuvant.