Newly identified networks of interconnected, fluid-filled chambers that line tissues throughout the human body may qualify as a completely new organ, researchers report in a study published Tuesday in Scientific Reports.

Researchers found the web-like tissue on the underside of skin, around the digestive tract, bladder, lungs, arteries, and within muscles. They speculate that the tissues—dubbed the “interstitium”—may act as “shock absorbers,” allowing our organs to swell and compress as we go about our business of breathing, eating, and living in general. The fluid it contains may also play heretofore unappreciated roles in basic biology and disease. For instance, the liquid could act as a conduit for cellular signals or harmful molecules, play a role in the development of edema (excessive fluid retention in tissues), and even help cancer cells spread.

The finding may “necessitate reconsideration of many of the normal functional activities of different organs and of disordered fluid dynamics in the setting of disease,” the authors conclude. And preliminary data “raises the possibility that direct sampling of the interstitial fluid could be a diagnostic tool,” they add.

The authors—led by gastroenterologist David Carr-Locke of Weill Cornell Medicine and pathologist Neil Theise of NYU Langone Health—lay out an explanation as to why this cushioning tissue has been missed in the past. That is, they note that standard methods to slice and fix tissues for close-up exams end up draining the interconnected chambers. The collagen-based supports around those spaces then collapse and stick together, creating the appearance of a dense, supportive tissue.

But Drs. Carr-Locke, Theise, and their colleagues weren’t using old-school methods to assess tissue when they made their discovery. They noticed the sodden layer fortuitously while using a new imaging technique called Probe-based Confocal Laser Endomicroscopy (pCLE) to assess bile duct tissue in patients. This technique allows researchers to image minute structures in living tissue with a camera and, generally, with a fluorescent tracer dye.

With the pCLE, the researchers noticed an odd “reticular pattern” in the tissue around the bile duct they were examining. The patterned tissue had dark, branching bands surrounding large, dye-filled polygonal spaces.

To confirm the weird find, the team turned to surgically removed tissue samples. They flash-froze the sample and cut the tissue perpendicular to the chambers. This allowed them to again see the sodden, mesh-like tissue layer. Knowing what to look for, they quickly found the watery chambers around other tissues and organs in the body. They also found evidence from some of their samples that cancer cells could get into the interstitium and move around.

While the findings are intriguing, they'll have to be confirmed by other researchers and discussed before the interstitium is in the running for being deemed a new organ. For now, Carr-Locke, Theise, and colleagues are focused on trying to figure out the structures and functions of the cells in their soggy find.

Scientific Reports, 2018. DOI: 10.1038/s41598-018-23062-6 (About DOIs).