Scientists Discover New Organ in the Human Body

Scientists have discovered a new immune organ structure within the skull bone that is believed to serve as the body’s first line of defence against brain cancer. The finding could potentially open new ways to treat brain tumours without the need for major brain surgery.

The discovery stems from research by biologists at Washington University (WashU) School of Medicine in St. Louis, United States. In a study published in the journal Nature, researchers identified a previously unknown immune system structure located inside the skull bone.

For now, scientists have only found the structure in mice. However, they have uncovered several clues suggesting that a similar structure likely also exists in humans.

The researchers suspect this structure functions like a ‘security post’ for the brain. Its proximity to brain tissue allows the immune system to respond to threats more quickly, including when cancer cells emerge.

‘This study reveals that skull bone marrow is far more than just a structural framework. It has a specialised immune response centre for the brain that was previously unrecognised,’ said Jonathan Kipnis, a brain immunologist at WashU and senior author of the study, as quoted from ScienceAlert on Thursday (20/8/2026).

According to Kipnis, the discovery changes the understanding of the relationship between the nervous system and the immune system. The structure also opens new opportunities for developing therapies for brain tumours and various neurological diseases.

Scientists have long understood that the human body has an immune system operating outside the central nervous system as well as a specialised defence mechanism for the brain and spinal cord. The two systems were previously considered relatively separate. In fact, the entry of immune cells from the peripheral system into the brain under certain conditions can cause problems because neural tissue is highly sensitive to immune responses.

However, research in recent years has shown a closer connection between the two. In previous work, the WashU team found small channels connecting brain tissue with the skull bone. These channels pass through the dura mater, the outermost protective layer surrounding the brain, before reaching the skull bone.

In the latest study, researchers used fluorescent tracer proteins to observe how molecules move through these channels. They then followed the movement of molecules from neurons until they reached the bone marrow inside the skull.

The researchers ultimately found a structure resembling a germinal centre. Such structures are normally found in lymph nodes and serve as ‘training grounds’ for immune cells. Within these structures, immature B cells can multiply in large numbers. The cells are then prepared to recognise specific threats before being dispatched to fight pathogens.

The difference is that the structure found in this study is located very close to the brain. This condition allows the immune system to mount a direct response without having to rely on recruiting cells from other parts of the body.

‘We have never seen a structure like this in healthy bone marrow before,’ said Jang Hyun Park, a cell biologist at WashU and first author of the study.

According to him, the finding suggests that the complex brain likely has its own immune structures to provide specialised protection.

To test the function of the structure, the researchers used mice with glioma, an aggressive type of brain cancer. They altered the activity of the lymphoid structures in the mice’s skulls by administering a hydrogel beneath the scalp. The hydrogel contained compounds that could either boost or suppress immune system activity.

The results were significant. Mice with disrupted skull lymphoid structures experienced far more aggressive tumour growth and had lower survival rates compared with the control group. Conversely, mice that received a combination of three immune-stimulating proteins showed a stronger immune response in the structure. Their immune systems were then able to fight the cancer more effectively and significantly improved their chances of survival.

Nevertheless, the researchers caution that results from mouse studies do not necessarily apply identically to humans. Still, there is an important clue. Researchers have previously found follicular T cells inside human skull bone marrow. That finding could be an indication that a similar immune structure is also hidden inside the human head.

If its existence in humans can be confirmed, the discovery could change how doctors treat brain cancer. One possible therapy is to use a hydrogel injected beneath the scalp to activate the immune centre. In theory, this method is far less invasive than brain surgery to remove a tumour.

‘This discovery fundamentally changes our understanding of neuroimmunology,’ said Kipnis.

He said the understanding that the brain has a ‘first army’ in the surrounding skull bone could change how scientists develop therapies for various neurological diseases. Beyond brain cancer, the approach could potentially be investigated for diseases such as Alzheimer’s, Parkinson’s, schizophrenia, and even long Covid, which have immune system-related components.

The researchers believe future therapies could even target these immune centres directly through the skull bone, thereby reducing side effects that arise in other parts of the body.