What role does the immune system play in hypertension?

Data obtained from the CDC indicates about 75 million people suffering from Hypertension in US alone

(Web Desk) - Millions of people have been suffering from hypertension across the world, and without proper management or treatment it can contribute to the risk of heart disease and even stroke.

Data obtained from the Centers for Disease Control and Prevention (CDC) has indicated that approximately 75 million adults in the US have been suffering from hypertension.

The American Heart Association (AHA) guidelines from 2017 define "hypertension" as systolic blood pressure (during a heartbeat) of 130 millimeters of mercury (mm Hg) or higher and diastolic blood pressure (when the heart is resting) of 80 mm Hg or higher.

The AHA has further determined lack of physical activity, an unhealthful diet, high cholesterol, and stress as some of the primary modifiable factors which contribute to the risk of hypertension.

New research by scientists at the University of Edinburgh in the United Kingdom has now unveiled another factor that seems to play a critical role in the development of hypertension.

The study, which the British Heart Foundation funded, has found that a type of specialized immune cell could make a real difference to the risk of hypertension.

"Hypertension affects millions of people across the globe, including 70 percent of people over 70," lead researcher Prof Matthew Bailey said.

"Our discovery sheds light on risk factors and, crucially, opens routes to investigate new drugs that could help patients," he said.

Prof Bailey and his team findings are now available online and are even presented in the European Heart Journal.

In the new study, the researchers experimented on mouse models and zeroed in on macrophages, a type of white blood cell that forms part of the immune system.

The role of macrophages is to identify and "eat up" foreign bodies that are present due to injury and infection.

The immune cells also "eat" cellular debris, which consists of the remains of cells that are no longer functional.

The current research has now uncovered a new role that macrophages play. It seems that they also consume molecules of endothelin, which is a hormone that acts as a vasoconstrictor, meaning that it can stimulate blood vessels to narrow.

Prof Bailey and his team explained that by controlling blood levels of endothelin, macrophages could ensure that blood vessels relax properly, and thus helps to reduce blood pressure.

The researchers verified this mechanism by feeding mice with lowered blood macrophage levels a high-salt diet (which increases the risk of high blood pressure) and monitoring their physiological reactions.

These rodents, the researchers soon found, experienced high blood pressure. However, when the team allowed macrophage levels to return to normal, the mice s blood pressure became healthy again, which suggests that the specialist white blood cells had an important role to play.

When they repeated the experiment in the mice which they had genetically modified to have poor endothelin system functioning, the findings remained consistent.

The researchers further verified the link between macrophages and blood pressure in rodents with drug-induced hypertension.

To analyse whether these findings were also valid in humans, the research team examined macrophage activity in individuals who took drugs for the management of antineutrophil cytoplasmic antibody vasculitis, a condition that affects the immune system and damages blood vessels.

The scientists found that the drugs that lowered macrophage levels, such as cyclophosphamide, led to higher blood pressure in the people who took them.

The findings, according to Prof Bailey and team, could help doctors better identify people who are most at the risk of hypertension, and they could be facilitated to new and improved therapies for high blood pressure.

Still, the researchers caution that further studies are necessary before the interaction between macrophages and endothelin can get the go-ahead as a therapeutic target.

"Our next steps will be to investigate the role of macrophages in people living with hypertension," Prof Bailey said.

"Undiagnosed high blood pressure causes damage to the heart and blood vessels, putting you at risk of a potentially fatal heart attack or stroke. But, we still don t fully understand all the mechanisms that lead to high blood pressure," Jeremy Pearson added, who is the associate medical director of the British Heart Foundation, who was not involved in the study.

This study shows for the first time that macrophages — a type of cell that helps regulate our immune responses — can be involved in the control of blood pressure. More research is needed but these cells could be a new target for drugs to treat the condition.