New Organ Found in Human Body and probably the largest organ

A team of researchers from New York University School of Medicine, Mount Sinai Beth Israel Medical Center, the Feinstein Institute for Medical Research and the University of Pennsylvania has identified that layers of the human body long thought to be connective tissues — below the skin’s surface, lining the digestive tract, lungs, and urinary systems, and surrounding arteries, veins, and the fascia between muscles — are actually interconnected, fluid-filled compartments, categorizing them as an organ.

The newfound organ — the interstitium (connective tissue) — is a series of spaces, supported by a meshwork of strong (collagen) and flexible (elastin) connective tissue proteins found below the skin’s surface, lining the digestive tract, lungs and urinary systems, and surrounding arteries, veins, and the fascia between muscles.

Importantly, the finding that this layer is a highway of moving fluid may explain why cancer that invades it becomes much more likely to spread.

Draining into the lymphatic system, the newfound network is the source of lymph, the fluid vital to the functioning of immune cells that generate inflammation.

Furthermore, the cells that reside in the space, and collagen bundles they line, change with age, and may contribute to the wrinkling of skin, the stiffening of limbs, and the progression of fibrotic, sclerotic, and inflammatory diseases.

“Techniques in processing tissue from surgery and biopsies failed to identify this space because it was artificially collapsed during the fixation process, or when tissue is prepared to view under a microscope,” the researchers said.

“As a result, scientists often interpreted the appearance of the submucosal space and this interstitium as a dense network of collagen or protein found in connective tissue, when in fact it was quite the opposite.”

“This discovery is extremely exciting because we’ve defined novel microanatomy and have laid the groundwork for how this may begin to explain cancer spread, inflammation and scarring of connective tissue,” said study co-lead author Dr. Petros Constantinos Benias, from the Feinstein Institute and Donald and Barbara Zucker School of Medicine at Hofstra/Northwell Health.

“This discovery will open up new research pathways for inflammation and cancer progression.”

“We are optimistic that with what we learned, we’ll soon be able to study and target the interstitial space for diagnosis of disease and perhaps for novel personalized treatments.”

According to the team, no one saw these spaces before because of the medical field’s dependence on the examination of fixed tissue on microscope slides, believed to offer the most accurate view of biological reality.

Scientists prepare tissue this examination by treating it with chemicals, slicing it thinly, and dying it to highlight key features. The ‘fixing’ process makes vivid details of cells and structures, but drains away any fluid.

Dr. Benias and colleagues found that the removal of fluid as slides are made causes the connective protein meshwork surrounding once fluid-filled compartments to pancake, like the floors of a collapsed building.

“This fixation artifact of collapse has made a fluid-filled tissue type throughout the body appear solid in biopsy slides for decades, and our results correct for this to expand the anatomy of most tissues,” said co-senior author Professor Neil D. Theise, from the Department of Pathology at NYU Langone Health.

“This finding has potential to drive dramatic advances in medicine, including the possibility that the direct sampling of interstitial fluid may become a powerful diagnostic tool.”

The research appears in the journal Scientific Reports.