Potential new function of the lymphatic system: producing blood

Scientists investigating lymphoedema have made a major discovery, revealing that lymphatic vessels can produce red and white blood cells. Until now, it was believed that blood cells derived solely from stem cells found in bone marrow.

The international team of researchers made the connection when investigating the causes of lymphoedema — a blockage in the lymphatic system resulting in swelling in the arm or leg, which is very difficult to treat. Lymphatic vessels are a key component of the cardiovascular system, responsible for returning excessive tissue fluid and protein (lymph) back to the bloodstream and forming a major part of the immune system that defends the body against harmful bacteria or viruses.

Led by the University of South Australia’s Professor Natasha Harvey, the scientists traced defects in the lymphatic vessels to cells being incorrectly programmed during development. Harvey said, “We discovered a site in DNA important for controlling genes that program the identity and development of lymphatic vessels.

“If these genes aren’t switched on at the correct time and place, lymphatic vessels don’t form properly, causing lymph fluid to leak back into the tissues, leading to swelling (lymphoedema). In an unexpected discovery, we identified that the same gene that controls the development of lymphatic vessels also controls the production of blood cells.”

According to Harvey, the team’s discovery suggests that lymphatic vessels may be a previously unrecognised source of blood cells both during development and in disease. The ability of lymphatic vessels to produce blood cells could thus be important for fighting infection and may play a role in some blood cancers.

With their study now published in the journal Nature, the researchers will next investigate what triggers lymphatic vessels to produce different types of blood cells and when this occurs — during normal development as well as during disease.

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