PhotoA healthy immune system is important to maintaining overall health, but sometimes it can also cause problems in the body instead of helping you heal. Researchers have discovered that there are two types of immune cells in the heart: ones that helps you heal and recover, and ones that cause inflammation and cause problems for sustained heart health.

 These two different immune cells are called macrophages. Up until now, the medical and scientific communities believed that all macrophages were the same, but researchers from Washington University School of Medicine in St. Louis have found otherwise.

 “Macrophages have long been thought of as a single type of cell…Our study shows there actually are many different types of macrophages that originate in different places in the body. Some are protective and can help blood vessels grow and regenerate tissue. Others are inflammatory and can contribute to damage,” said Slava Epelman, who led the study. 

Healing vs. inflammation

The long-standing idea was that all macrophages were developed in bone marrow. They would then travel to different areas of the body depending on what job needed to be done, such as helping to fight off disease or digesting dead cells.

“Now we know it’s more complicated,” said Epelman. “We found that the heart is one of the few organs with a pool of macrophages formed in the embryo and maintained into adulthood. The heart, brain and liver are the only organs that contain large numbers of macrophages that originated in the yolk sac, in very early stages of development, and we think these macrophages tend to be protective.”

Epelman and her team made this discovery through studying mice. They found that when the mice went through types of cardiac stress (i.e. high blood pressure, heart attack, etc.) then macrophages in the blood would come to the heart and overpower the embryonic macrophages that were already there. This can be dangerous, since macrophages from the blood can often lead to inflammation, whereas the embryonic macrophages help with healing.

“Now that we can tell the difference between these two types of macrophages, we can try targeting one but not the other,” said Epelman. “We want to try blocking the adult macrophages from the blood, which appear to be more inflammatory. And we want to encourage the embryonic macrophages that are already in the heart to proliferate in response to stress because they do things that are beneficial, helping the heart regenerate.” 

Promising, but not a cure-all

Epelman and her colleagues explain that embryonic macrophages promote healing because they were formed before birth and contributed to the healthy formation of different organs and other parts of the body. Macrophages found in the blood formed well after this time and are better equipped at fighting foreign contaminants. They cause inflammation since that is the body’s natural reaction to dealing with infection.

Researchers believe that this discovery may provide an answer for why some people are able to heal better than others after a heart attack. People with diabetes, for example, have macrophages that have been altered by their disease. As a result, their hearts often do not heal as well after cardiac events.

Although the discovery may open new avenues for rehabilitation after heart trauma, Epelman and her colleagues want to stress that macrophages are not a cure-all for cardiac problems. “Long established heart failure doesn’t recover…But in the first few months after injury, there’s a real potential to impact the heart’s recovery,” she said. 

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