New Human ‘Organ’ Was Hiding in Plain Sight

The interstitium, scientists found, is under our skin and between our organs. Understanding it may eventually help treat disease.

By Sarah Gibbens
PUBLISHED March 27, 2018

Lurking just underyour skin might be a new organ only now identified for the first time, say a team of scientists.
In a new study published in the journal Scientific Reports, researchers from New York University’s School of Medicine say they have found a new organ they’re calling the “interstitium.”

It’s nearly everywhere—just below the skin’s surface, surrounding arteries and veins, casing the fibrous tissue between muscles, and lining our digestive tracts, lungs, and urinary systems.

It looks like a mesh. The interstitium is a layer of fluid-filled compartments strung together in a web of collagen and a flexible protein called elastin. Previously, scientists thought the layer was simply dense connective tissue.

The organ has seemingly been hidden in plain sight, and scientists say they missed it because of the way tissue is studied. Before being placed under a microscope, samples are thinly sliced and treated with chemicals that allow researchers to identify key components more easily. While the process is helpful for more easily spotting details, it drains fluid from the sample.

Bottom of Form

Devoid of their fluid, the compartments collapse, like a building with the floors suddenly knocked out, leaving the whole structure to flatten like a pancake.

To find these pockets of interstitial fluid, medical researchers looked at living tissue instead of sampling dead tissue samples. They did this by using a probing technique called confocal laser endomicroscopy. The method entails using a tiny camera probe that takes a microscopic look around a human body. Tissue is lit by the endoscope’s lasers and the fluorescent patterns it then reflects are analyzed by sensors.

Accidental Discovery

Scientists first noticed the compartments when looking at a bile duct. They saw what they thought might be tears in dense tissue. The images were taken to Neil Theise, a professor at NYU’s School of Medicine and author on the paper.

“You’re talking about the remaining extracellular fluid that’s unaccounted for,” Theise says. About 70 percent of the human body is made of water, and about two thirds of that is found in cells. The remaining third, says Theise, is only partially known.

In addition to accounting for bodily fluid, the compartments may help explain essential functions.

“It’s like a shock absorber,” says Theise. “Not a hard, stiff material.”

Among Theise’s theories for the purpose of the interstitium is that it’s a source of lymph, a fluid that moves through the body’s lymphatic system and supports immunity. He says that knowing how diseases spread through this part of the body could help researchers better understand how cancer spreads.

“Can we detect [disease] earlier by sampling fluid from the space? Can we figure out mechanisms to stop spread?” He asks.

Promise and Skepticism

Jennifer Munsonis a biomedical engineer at Virginia Tech who has looked at fluid in the body. She was not involved with the study but says its findings are promising.

“I think what the paper shows is the benefit of having new ways to image and look at tissues. [Previous methods] dehydrate the tissues, and you lose so much structural information,” Munson notes.

She says she’s fairly convinced these structures exist but wants to see more research before speculating on what they do, and whether its accurate to call them a new organ.

“I’m really excited about the find but, as with all scientists, I approach everything with a little skepticism,” she adds.

Theise says he’s aware of some of the skepticism surrounding his findings, but it’s territory he’s not shy about wading into. In 2005, he wrote an essay in Naturechallenging the importance of “cell theory”—a concept that holds cells as the basic structure of all organisms, and in 2001, he published a paperfinding that adult stem cells could be made to act similarly to embryonic cells.

By Alice Park
March 27, 2018

It’s not a second stomach or a mini-brain. But scientists have discovered an important new organ that may play a critical role in how many tissues and other organs do their jobs, as well as in some diseases like cancer.

In a study published in Scientific Reports, a New York University-led team of researchers describe the interstitium, which is a series of connected, fluid-filled spaces found under skin as well as throughout the gut, lungs, blood vessels and muscles.

The bubble wrap-like network only became visible when the pathologists used a new laser endoscope, called a confocal laser endomicroscope, that allowed them to see microscopic tissues in living people. Most studies of tissues missed the interstitium because they rely on biopsies of tissues that are then dried and fixed onto microscope slides; the desiccated samples never showed the fluid-filled spaces.

But when the endoscopic laser was used to remove the pancreas and bile duct in a dozen patients with cancer, the odd spaces became obvious.

In the study, the authors speculate that the spaces could be important for a number of functions, including generating the collagen that supports cells in certain tissues, as well as housing the stem cells that rush in to repair damaged tissues. They may also play a role in conducting electrical signals as cells move and stretch. Because the spaces form a fluid-highway linking tissues and organs, it may also explain why some cancers, if they invade the spaces, spread more quickly than others.