Dictyosphaerium chlorelloides is a green microalga from the Chlorella clade that produces highly viscous exocellular polysaccharides. The cell wall polysaccharides of this alga have not been studied in detail. In this article, water-soluble polysaccharides from D. chlorelloides biomass were extracted with hot water and purified by preparative chromatography. The composition, structural features and molecular masses of subsequently eluted fractions F1, F2, F3, F4 and F5 (minor) were determined. Three high-yield products F1, F3 and F4 consisted mainly of galactopyranosyl, 2-O-methyl-galactopyranosyl, rhamnopyranosyl and mannopyranosyl units at different proportions, while F2 was rich in glucose. Immunoactivity of these fractions was evidenced in a mixed population of immune cells derived from mice spleens after incubation with polysaccharides by flow cytometry, MTT and Immunospot assays. These fractions, except F2, demonstrated selective immunostimulant activity, and the F1 fraction induced the most potent effect, closely followed by the F3 and F4 fractions. The in vivo mechanism of their action is associated with the activation of innate immunity and shapes the immune response to the Th1 type.

Department of Biotechnology Faculty of Food and Biochemical Technology University of Chemistry and Technology Prague Technická 5 166 28 Prague 6 Dejvice Czech Republic; EcoFuel Laboratories s r o Ocelářská 9 Prague 9 Libeň 190 00 Czech Republic

Department of Carbohydrates and Cereals Faculty of Food and Biochemical Technology University of Chemistry and Technology Prague Technická 5 166 28 Prague 6 Dejvice Czech Republic

Department of Carbohydrates and Cereals Faculty of Food and Biochemical Technology University of Chemistry and Technology Prague Technická 5 166 28 Prague 6 Dejvice Czech Republic; Laboratory of Immunotherapy Institute of Microbiology Czech Academy of Sciences Vídeňská 1083 142 20 Prague 4 Krč Czech Republic

Institute of Chemistry Slovak Academy of Sciences Dúbravská cesta 9 845 38 Bratislava Slovakia

Institute of Organic Chemistry and Biochemistry AS CR Flemingovo sq 2 166 28 Prague 6 Czech Republic

Laboratory of Immunotherapy Institute of Microbiology Czech Academy of Sciences Vídeňská 1083 142 20 Prague 4 Krč Czech Republic

Laboratory of Immunotherapy Institute of Microbiology Czech Academy of Sciences Vídeňská 1083 142 20 Prague 4 Krč Czech Republic; Department of Cell Biology Faculty of Science Charles University Albertov 6 128 00 Prague 2 Czech Republic

Laboratory of Immunotherapy Institute of Microbiology Czech Academy of Sciences Vídeňská 1083 142 20 Prague 4 Krč Czech Republic; Department of Immunology 2nd Faculty of Medicine Charles University and Motol University Hospital 5 Úvalu 84 150 06 Prague 5 Czech Republic

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