Immune cells could mend broken hearts

A new research has revealed that immune system plays an important role in the heart's response to injury, suggesting that embryonic macrophages in the heart promote healing after injury.

Now, researchers at Washington University School of Medicine in St. Louis 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," first author Slava Epelman, MD, PhD, instructor in medicine, said. "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."

Epelman said they 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 they think these macrophages tend to be protective.

Studying mice, Epelman and his colleagues showed that 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 study is published in the journal Immunity.