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Researchers have found a way to get heart's inherent immune cells to repair cardiac tissue.

Following injury, two types of immune cells or macrophages enter the heart. One is from the bone marrow and the other is heart's innate macrophages. It was long known that neonatal hearts could repair successfully but adult hearts could not. Through the recent study conducted in mice, researchers were able to show that heart's innate cells are responsible in repairing neonatal hearts while bone marrow macrophages further damaged the tissue by causing inflammation.

"Researchers have known for a long time that the neonatal mouse heart can recover well from injury, and in some cases can even regenerate". If you cut off the lower tip of the neonatal mouse heart, it can grow back. But if you do the same thing to an adult mouse heart, it forms scar tissue," said first author Kory J. Lavine in a press release. 

The research team then set out to improve heart recovery by blocking entry of bone marrow immune cells into heart post injury. This they did by using a compound that blocks a protein called CRR2 which is present on bone marrow cells but not on heart immune cells. On blocking this protein, the bone marrow cells did not enter the heart.

"When we did that, we found that the macrophages from the bone marrow did not come in. And the macrophages native to the heart remained. We saw reduced inflammation in these injured adult hearts, less oxidative damage and improved repair. We also saw new blood vessel growth. By blocking the CCR2 signaling, we were able to keep the resident macrophages around and promote repair," Lavine said. The researchers caused heart damage in mice mimicking human heart failure.

"We have identified similar immune cell subtypes that are present in the human heart. We need to find out more about their roles in heart failure in patients and understand more about how macrophages that reside in the heart promote repair," Lavine said. 

The findings have been published in Proceedings of the National Academy of Sciences.