Inflammation contributes to the hardening and narrowing of the arteries known as atherosclerosis. Atherosclerosis is a condition that can result in heart attack or stroke. Researchers at La Jolla Institute for Allergy and Immunology looked at the roles that immune cells play in this process and how the function of different immune cells can change as atherosclerosis progresses. Different subtypes of immune cells have opposing roles in atherosclerosis – some add to the buildup of plaque, and others prevent it.
"People think atherosclerosis is just about cholesterol, diet, and exercise, but it's actually an immune disease," said Dalia Gaddis, Ph.D., one of the researchers. "The blockage of arteries is very much due to the immune system reacting to excess cholesterol and lipids in the walls of blood vessels."
In the study, Gaddis and her team investigated the protective cells called regulatory T cells, also known as Tregs, which are known to prevent the development of atherosclerosis. They also aimed to track regulatory T cells in mice during the turning of protective cells into promoters of inflammation. Then, they fed one group of mice with a Western diet, which is typically composed of foods high in fat and cholesterol, for 15 weeks. On the other hand, another group of mice were fed with a control treatment. After that, they analyzed the immune cells of the mice.
The researchers found that when mice were fed with the high-fat Western diet, their numbers of protective Tregs decreased. In addition, the mice fed with the Western diet had significant numbers of former regulatory T cells in the lymph nodes and aorta. Moreover, molecular analyses showed that some of these "ex T cells" became follicular helper T cells (Tfh). As they further experimented, they concluded that these Tfh cells promote atherosclerosis.
They also examined whether HDL, which eliminates excess cholesterol from cells, might prevent atherosclerosis by inhibiting the loss of regulatory T cells. To test this idea, they administered apolipoprotein AI, the primary component of HDL, to the mice. Results showed that regulatory T cells fought the effects of the Western diet and did not turn into Tfh cells. The HDL help protect immune cells keep their identity and maintain clear arteries. (Related: Atherosclerosis and inflammation: How to overcome it naturally.)
"With a western diet, protective cells change to damaging cells, causing more inflammation," said Gaddis. "What we're finding is that HDL – the good cholesterol – actually helps shield the protective cells against the damaging changes that occur during atherosclerosis plaque development."
Having high HDL levels have several health benefits. One of these is that it helps transport cholesterol from the arteries to the liver where it can be used or excreted. Good cholesterol also provides antioxidant and anti-inflammatory activity, and is associated with a lower risk of heart disease. In order to increase your HDL cholesterol levels, you can do the following:
Read more news stories and studies on protecting the heart by going to Heart.news.