Researchers here dig in to the details of one of the mechanisms that might explain variations in the ability to heal from heart injuries - and which might be manipulated to improve the situation:
The immune system plays an important role in the heart's response to injury. But until recently, confusing data made it difficult to distinguish the immune factors that encourage the heart to heal following a heart attack, for example, from those that lead to further damage. Now, [researchers] have shown that two major pools of immune cells are at work in the heart. Both belong to a class of cells known as macrophages. One appears to promote healing, while the other likely drives inflammation, which is detrimental to long-term heart function.
"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. 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."
Healthy hearts maintain this population of embryonic macrophages, as well as a smaller pool of adult macrophages derived from the blood. But during cardiac stress such as high blood pressure, not only were more adult macrophages recruited from the blood and brought to the heart, they actually replaced the embryonic macrophages. The complex interplay between these immune cells in the heart may provide an explanation for why some people experience healing following a heart attack but others don't.
"Now that we can tell the difference between these two types of macrophages, we can try targeting one but not the other. 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."