Royal Agaricus (Agaricus blazei) Also known as the "Sun Mushroom," grows in mountainous rainforests near Piedade, Brazil. There it is called "Cogumelo de Deus" ("Mushroom of God") because it has been related to lower incidence of adult diseases in that region.
Royal Agaricus does indeed have a higher polysaccharide content than other mushrooms. Royal Agaricus supplements are extremely popular in Japan for immune system enhancement.
Agaricus mushroom is used for cancer, type 2 diabetes, high cholesterol, “hardening of the arteries” (arteriosclerosis), ongoing liver disease, bloodstream disorders, and digestive problems. Other uses include prevention of heart disease, weakened bones (osteoporosis), and stomach ulcers. It is also used to boost the immune system and for physical and emotional stress.
WebMD: Insufficient evidence to rate effectiveness for the above.