In 2018, several research teams discovered “new” human structures or pathways, several of which appear to allow immune cells (and the microbes that infect them) to bypass the classical “blood brain barrier.” The findings also suggest that the human body is much less compartmentalized than previously believed. Here are some of the top 2018 studies on the topic:

Functional aspects of meningeal lymphatics in ageing and Alzheimer’s disease

Lead author: Jonathan Kipnis, University of Virginia

In 2015, Jonathan Kipness and team became one of two research groups to demonstrate the existence of previously undiscovered meningeal lymphatic vessels. These fluid pathways connect the cerebrospinal fluid and cervical lymph nodes directly to the brain. In this follow-up study, the team found that dysfunction of meningeal vessel drainage increased Alzheimer’s pathology in mice.

Paper highlight: “…augmentation of meningeal lymphatic function might be a promising therapeutic target for preventing or delaying age-associated neurological diseases.”

Structure and Distribution of an Unrecognized Interstitium in Human Tissues

Lead author: Neil Theise, Mount Sinai Beth Israel Medical Center

The interstitium is shown above as the light pink layer at the bottom of this image.
Credit: Eric V. Grave/Getty

This study documents a previously uncharacterized fluid-filled lattice of collagen bundles that connects all human tissues. This “human interstitium” may be even be classified as a new organ. And because the interstitium drains directly into the lymph nodes, it may also connect immune cells + microbes to the central nervous system.

Direct vascular channels connect skull bone marrow and the brain surface enabling myeloid cell migration

Lead author: Matthias Nahrendorf, Massachusetts General Hospital and Harvard Medical School

The team identified microscopic channels that connect skull bone marrow to the lining of the brain. Under conditions of inflammation these channels transport neutrophils (and possibly associated pathogens) directly from the marrow into the brain.

The vermiform appendix impacts the risk of developing Parkinson’s disease

Lead author: Viviane Labrie, Van Andel Research Institute, Michigan

The team found that, instead of being a “useless organ,” the appendix appears to be an immune tissue responsible for the sampling and monitoring of pathogens. They also found that appendix surgical samples removed from patients with Parkinson’s disease contained alpha-synuclein, suggesting that the Parkinson’s disease process might involve the appendix. Since alpha-synuclein appears to have potent antimicrobial activity, the findings further support a role for chronic infection in Parkinson’s.