Glucans from mushrooms protect against virus infections
Eating several types of mushrooms every day may protect against potentially deadly flu viruses. This is suggested by an animal study that American researchers at the University of Louisville published in the Annals of Translational Medicine a few years ago. According to the study, glucans not only make the innate immune system more aggressive, but they also speed up the production of antibodies by the adaptive part of the immune system.

The researchers gave mice glucans from medicinal mushrooms every day for 2 weeks. The researchers had compiled the extract themselves. The glucans came from the Siberian chaga, Agaricus blazei [a mushroom closely related to the ordinary button mushroom], shiitake, reishi and maitake.In an earlier published animal study, the researchers demonstrated that a combination of glucans from different mushrooms can stimulate the immune system more strongly than supplementation with glucans from one specific mushroom. [Ann Transl Med. 2014;2(2):14.]
If the mice had been humans, they would have received roughly 200 milligrams of mushroom glucans daily. You could also get this amount if you eat a normal portion of edible mushrooms every day.

Mice in a control group received no glucans.
After 14 days, the researchers infected the mice through the nose with the influenza virus H5N1A/HK483.
12 days after infection with the virus, all mice in the control group [Influenza] were dead, but 80 percent of the animals in the supplementation group [Glucan] were still alive.

The figure above [click for a larger version] shows that supplementation with mushroom glucans activated the NK cells and increased the amount of inflammatory proteins as interferon gamma in the lungs. This indicates that glucans make the immune system more aggressive.Supplementation increased the production of antibodies. This suggests that the mushroom glucans not only stimulate the innate immune system, but also the acquired immune system. It is therefore not surprising that the researchers found fewer viruses in the lungs of the animals in the supplementation group than in the lungs of the mice in the control group.

In organs such as the thymus and the heart, supplementation with mushroom glucans also reduced the number of viruses.

"In summary, the current study showed that dietary glucan can significantly reduce the effects of influenza infection", the researchers summarize. "Lower mortality and overall effects of infection are most probably affected by stimulation of both cellular and humoral responses leading to the lower viral load in many organs."

"These results suggest that consumption of dietary glucan might be potentially useful as a complementary or alternative approach to treatment of influenza infection."
Ann Transl Med 2015;3(2):22.