Check out this PDF file titled Advances in Mushroom Research in the Last Decade.
D-fraction has the unique polysaccharide structure and the degree of branching is greater than any beta-glucan found in any other medicinal mushrooms that demonstrate similar immune stimulatory properties. Researchers theorize that the complexity of branching makes Maitake superior to other medicinal mushrooms in immune stimulatory effect. One of the difficulties with many of the medicinal mushrooms is that they lose much of their effectiveness when taken orally. An essential point about the D-fraction is that current research indicates it is most effective when consumed orally.