On Thursday, 2 October 2025, Monica Daugbjerg Christensen will defend her doctoral thesis in Food Science at the Faculty of Food Science and Nutrition at the University of Iceland. The thesis is entitled: Refining Marine Polysaccharides and Their Immunomodulatory Effects.
The opponents are Dr. Kari Tvete Inngjerdingen, Associate Professor at the University of Oslo, and Dr. Finn Aachmann, Professor at the Norwegian University of Science and Technology.
The supervisors were Hildur Inga Sveinsdóttir, Lecturer, and Guðjón Þorkelsson, Professor. The advisors were Guðmundur Óli Hreggviðsson, Professor and Strategic Specialist, and Jóna Freysdóttir, Professor. Also serving on the doctoral committee were Ólafur H. Friðjónsson, Research Manager, and Eva Nordberg Karlsson, Professor.
Ingibjörg Gunnarsdóttir, Professor and Deputy Head of the Faculty of Food Science and Nutrition, will chair the ceremony, which will take place in the Ceremonial Hall of the University of Iceland and begins at 13:30.
Abstract
Brown algae contain large quantities of diverse polysaccharides with a wide range of biological activities. In this doctoral project, four approaches were investigated into how enzymes can be used to modify marine polysaccharides and their effects on the immune system. 1) A novel sulfatase, SulA1, from the marine bacterium Arthrobacter, was produced using recombinant methods and studied in detail. The SulA1 sulfatase was able to remove a sulfate group from N-Acetyl-D-galactosamine-4-sulfate, reflecting its ability to remove sulfate groups and thereby alter the biological activity of polysaccharides. 2) Laminarin molecules from three species of brown algae (Laminaria digitata, L. hyperborea, and Saccharina latissima) were isolated and cleaved into oligosaccharides. The structure of the oligosaccharides was analysed, and it emerged that their size and branching affected cytokine secretion by dendritic cells and their ability to activate and differentiate T cells. These results suggest that laminarin molecules and their derivatives could potentially be used in the treatment of immune-related diseases. 3) Fucoidan from S. latissima was cleaved into oligosaccharides of different sizes. Short oligosaccharides had anti-inflammatory effects by reducing the secretion of pro-inflammatory cytokines by dendritic cells, thereby attenuating Th1 immune responses. They could therefore potentially be useful in the treatment of inflammatory diseases. 4) Two oligosaccharides derived from alginate increased cytokine secretion by dendritic cells and promoted Th1 responses of T cells in co-culture. This suggests that these oligosaccharides could be useful in enhancing immune responses, for example in cancer treatment or as immune adjuvants. Taken together, the results of this project demonstrate that enzymatic degradation of marine polysaccharides can affect the immunological activity of the degradation products, increasing the likelihood of their use in developing treatments for immune-related diseases. Furthermore, this could lead to more environmentally friendly enzymatic processing of polysaccharides from brown algae, which could increase their value and utility in the pharmaceutical and nutraceutical industries.