What role does the immune system play in hypertension?
20 January, 2019
Millions of people in the United States and across the world have hypertension, a condition that, without proper management, can contribute to the risk of heart disease and stroke.
Data from the Centers for Disease Control and Prevention (CDC) indicate that approximately 75 million adults in the U.S. live with hypertension.
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 also name lack of physical activity, an unhealthful diet, high cholesterol, and stress as some of the primary modifiable factors that increase the risk of hypertension.
New research by scientists at the University of Edinburgh in the United Kingdom has now uncovered another factor that seems to play a role in the development of this condition.
The study, which the British Heart Foundation funded, 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," says lead researcher Prof. Matthew Bailey.
"Our discovery sheds light on risk factors and, crucially, opens routes to investigate new drugs that could help patients," he adds.
Prof. Bailey and team's findings appear in the European Heart Journal, and they are available online.
Cellular debris-eaters and blood pressure
In the new study, the researchers worked with 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 colleagues explain that, by controlling blood levels of endothelin, macrophages can ensure that blood vessels properly relax, which helps lower 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 mice that 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.