There is increasing evidence that some polysaccharides of algae, fungi and plant cells walls may have immunemodulating effects of importance for health and medical therapy. A common feature of non-starch polysaccharides from algae, fungi and higher plants is that they stimulate the immune system, but with varying efficacy and presumably by different mechanisms.
For instance, mixed-linked ß-1,3:1,6-glucans from fungi (e.g. mushrooms) and yeast have been known as potent immunostimulants against infectious diseases and cancer. These ß-glucans stimulate macrophage, neutrophil, and NK cells via ß-glucan-specific receptor sites on their cell surface membranes (CR3 and dectin-1). When bound, ß-glucan activates these cells and sets off a cascade of immune defenses that protect the organism from microbial, viral, parasite and fungal infections, and result in antitumor and anticancer activity. However, much less is known about immunomodulating effects of mixed-linked ß-1,3:1,4-glucans from cereals.
It has been shown that oat ß-glucan alter neutrolphil respiratory burst activity, and although not fully confirmed it is speculated that oat ß-glucan may counteract the negative effect of fatiguing exercise and enhance the immunostimulatory effect of moderate exercise, and enhance resistance against bacterial and parasitic infections. A recent study with human ileosomists has shown that not only leukocytes, but also enterocytes (intestinal cells) have enhanced immune responses to consumption of oat ß-glucan. Whether this stimulatory effect contributes to enhanced protection of invading harmful pathogens is not known.
Barley ß-glucan given in the diet to mice has been shown to potentiate the effect of cancer therapy, leading to enhanced tumor regression and survival from experimentally induced tumors. In vitro studies have also shown that barley ß-glucan increases murine macrophage phagocytosis of Salmonella, and by extraction of mixed-linked-ß-1,3:1,4-glucan from rye it was found that ß-glucan with an average molecular weight of 18 900 Da was the most potent for stimulation of human monocytes to produce tumour necrosis factor (TNF).
Collectively, there are indications from in vitro and animal studies of immunostimulating effect of ß-glucans from cereals whereas the body of evidence from human trials to document any effect of consuming ß-glucan or ß-glucan-rich cereal products on the immune defence are not enough yet.
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