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11.02.2009

Button mushrooms make immune defences more alert

It could be that people who eat button mushrooms frequently are better protected against cancer, microbes and viruses. At least, that is what immunologists at Tufts University write in the Journal of Nutrition. Experiments they did on mouse cells point in this direction.

Button mushrooms, the researchers had already discovered in earlier experiments with mice, activate natural killer (NK) cells. The mushrooms increase the production of interferon and TNF-alpha in the cells. The immune cells use these proteins to kill cells that have started to proliferate.

NK cells are heavy-duty immune cells, and belong to the lymphocytes. When they discover cells they consider to be alien, they kill them. Their main targets are cells that have mutated into cancer cells and cells that are infected by a virus.

If the NK cells and other 'spontaneous' immune cells don't manage to deal with intruders or cancer cells, then the body calls in the 'intelligent' immune cells. This happens once the antigen presenting (AP) cells have passed on information to the intelligent immune cells about how to recognise the stubborn intruders.

The dendritic cells are the fastest working AP cells, immunologists suspect. These also stimulate the more primitive parts of the immune system, like the NK cells.

In their publication, the researchers examined the effect of button mushrooms on the dendritic cells in mice. They extracted the cells from the bone marrow of the mice, and then exposed the cells to button mushroom extracts and ovalbumin, a protein. The latter induces an immune response. The higher the concentration of the extract, the quicker the cells reacted.

In addition, the mushroom extracts led to an increase in interleukin 12 production in the dendritic cells. IL-12 induces the production of cell-killing compounds such as interferon in other immune cells.

The researchers also discovered that the dendritic cells taught other immune cells to react more quickly to the protein.

The researchers suggest that the stimulatory effect of button mushrooms on immune cells can be found in the mushrooms' sugar chains. Button mushrooms contain beta glucans – to be more precise beta 1,3 glucans with beta 1,6 side-chains. These compounds resemble the sugar chains found in the membranes of pathogens like bacteria. They are not found in animals – unless the animals have eaten mushrooms or toadstools. Scientists think that the glucans give the immune system a wake-up call.

Sources:
J Nutr. 2008 Mar;138(3):544-50.