We usually think of the lymphatic system as the body's clean-up and defence network. It helps move fluid around the body and plays an important role in the immune system. But scientists are finding that its role may be much bigger than that.

New research from Northwestern Medicine Illinois, suggests that lymphatic vessels in the heart can also send signals that help control how the developing heart grows. The finding could eventually offer clues about how the heart responds to damage, including after a heart attack. The study was published in Genes & Development in September 2026.

The surprising connection between the lymphatic system and the heart

The heart and lymphatic system may seem like completely separate parts of the body, but the new research suggests they communicate with each other during heart development.

Researchers found that lymphatic vessels release a protein called Reelin. This protein appears to help regulate several types of cells involved in the growth and development of the heart.

One of the important tissues involved is the epicardium, the thin outer layer that surrounds the heart. The epicardium plays an important role while the heart is developing and also interacts with other cells involved in building the heart's structure.

In simple terms, the lymphatic vessels appear to be sending instructions that help different parts of the developing heart grow and work together.

So, what is Reelin?

Reelin is a protein involved in communication between cells. Earlier work from the same research group found that Reelin released by cardiac lymphatic vessels helps promote the growth of heart muscle cells.

The latest study adds another piece to the picture. Researchers found that Reelin also appears to support the epicardium and certain fibroblasts, which are cells that help provide structure and support to the heart. The researchers also observed changes in two growth-related factors, WT1 and IGF-1, when Reelin was absent.

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Guillermo Oliver, PhD, senior author of the study and Thomas D. Spies Professor of Lymphatic Metabolism at Northwestern University Feinberg School of Medicine, said the findings reveal another regulatory network involved in heart growth.

What happens when this signal is missing?

The researchers used genetically modified mice to study what happens when lymphatic-derived Reelin is missing.

The animals developed problems with the epicardium and lost some populations of fibroblasts involved in supporting the heart. The researchers also found fewer epicardial cells showing activity of WT1 and IGF-1, both of which are involved in cardiac growth.

The team also used laboratory-grown human "epicardioids". These are three-dimensional models made from human cells that mimic some features of a developing heart. When the researchers treated these mini-heart models with Reelin, they saw increased expression of several markers associated with epicardial cells.

That gives scientists an additional clue that the same communication pathway may be relevant to human heart biology, although it does not prove that the process works the same way in people.

Could this help the heart after a heart attack?

This is perhaps the most interesting question, but it is also where the research needs to be put into perspective.

The researchers believe the findings could eventually help explain how the heart responds to injury. Oliver said some of the mechanisms involved in heart development may also matter when an adult heart is damaged.

"Some of the mechanisms that help control how the heart grows during development may also be important when the adult heart is injured," Oliver said.

The researchers suggest that Reelin may have a role in reactivating parts of the epicardium after injury, potentially helping the heart's repair processes. However, this is still an area for future research. The current study does not show that a Reelin-based treatment can repair a human heart after a heart attack.

Why does this matter?

One of the bigger questions in biology is how an organ knows when it has grown enough.

The Northwestern team proposes that lymphatic vessels could act somewhat like monitoring systems. As they develop alongside organs, they may sense changes in the surrounding tissue and send signals that influence growth.

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Oliver described the idea as lymphatics acting as "organ-level quality control systems", helping signal when tissues should continue growing and when they should stop.

It is an intriguing idea because it changes the way scientists think about lymphatic vessels. They may not simply be passive plumbing for moving fluid and immune cells. They may also communicate with other tissues and influence how organs develop and respond to injury.

What does this mean for everyday heart health?

For now, this research does not change the usual advice for looking after your heart. It is a basic science discovery about how the heart develops and how different cell systems communicate.

The possible applications, such as improving heart repair after a heart attack or understanding congenital heart defects, are still future possibilities rather than treatments available today. The study's experiments were performed using mouse models and laboratory-grown human heart-like organoids.

Also Read: Sudden cardiac arrest in young athletes: Why does it happen 

What the research does offer is a fascinating look at how much communication is happening inside the body, often between systems we do not normally think of as connected.

The heart, it turns out, may have a much more complicated relationship with the lymphatic system than scientists once realised.

(Disclaimer: This article is for general information only and does not replace medical advice. Always consult a doctor for medical concerns)