Researchers have found another good reason to eat your green vegetables: immune protection.
It turns out that green vegetables -- from bok choy to broccoli -- are the source of a chemical signal that is important to a fully functioning immune system. They do this by ensuring that immune cells in the gut and the skin known as intra-epithelial lymphocytes (IELs) function properly.
After feeding otherwise healthy mice a vegetable-poor diet for two to three weeks, the researchers saw 70 to 80 percent of these protective cells disappear. These protective IELs exist as a network beneath the barrier of epithelial cells covering inner and outer body surfaces, where they are important as a first line of defence and in wound repair.
The team found that the numbers of IELs depend on levels of a cell-surface protein called the aryl hydrocarbon receptor (AhR), which can be regulated by dietary ingredients found primarily in cruciferous vegetables. Mice lacking this receptor lose control over the microbes living on the intestinal surface, both in terms of their numbers and composition.
Earlier studies suggested that breakdown of cruciferous vegetables can yield a compound that can be converted into a molecule that triggers AhRs. The new work finds that mice fed a synthetic diet lacking this key compound experience a significant reduction in AhR activity and lose IELs.
With reduced numbers of these key immune cells, animals showed lower levels of antimicrobial proteins, heightened immune activation and greater susceptibility to injury. When the researchers intentionally damaged the intestinal surface in animals that didn't have normal AhR activity, the mice were not as quick to repair that damage.
The researchers say "it's tempting to extrapolate to humans, but there are many other factors that might play a role."
Even so, eating cruciferous vegetables on a regular basis - broccoli, bok choy, Brussels sprouts, cabbage, cauliflower, turnip - can help guard against stroke and cancers of the breast, lung prostate and pancreas.
Source: Cell, October 2011.
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