The present relation relates to a process of extracting immunostimulatory polysaccharides from food-grade microalgae. It also relates to methods of treatment and/or prophylaxis different disease disorders using the resulting inventive preparations. The immunostimulatory preparations extracted from microalgae comprising polysaccharides produced by extracting the microalgae with a solvent comprising water or a mixture of water and at least one lower alkyl alcohol where the alkyl portion is from 1 to 4 carbon atoms and in which active polysaccharides have apparent molecular weights above approximately 2 million daltons.
