Scientists have identified a new mechanism of the brain's immune defense

Structures resembling lymph nodes and involved in the protection of the central nervous system were found in the bone marrow of the mouse skull. In the glioblastoma model, disruption of their work accelerated tumor growth and shortened the life span of animals, and increased local immune response helped the body to more effectively reject tumor cells. About how the bone marrow of the skull participates in the immune defense of the brain and whether the discovery can be used to treat people, see the "Izvestia" material.

What immune structures were found in the skull

Researchers at Washington University School of Medicine in St. Louis have identified organized clusters of immune cells in the bone marrow of the mouse skull. In terms of structure and tasks performed, they resembled structures that are usually found in lymph nodes.

Inside such clusters, scientists have found formations similar to the germinal centers of lymph nodes, as well as a special population of T-helper cells. These cells help activate B lymphocytes, which are involved in the production of antibodies and the formation of a humoral immune response.

The authors of the scientific work call the found formations lymphoid structures of the bone marrow of the skull. The expression "immune organ" used in the research reports is figurative: scientists have not announced the discovery of a separate anatomical organ in humans.

How the brain transmits signals to the immune system

Previously, it was believed that the brain is largely separate from the immune system. However, subsequent studies have revealed lymphatic vessels in the dura mater, located directly under the skull, as well as microscopic channels connecting the bone marrow of the skull, meninges and brain tissue.

Immune cells, cerebrospinal fluid, and cellular metabolic products can move through these channels. In the new work, the researchers tracked how proteins from the brains of mice passed through similar pathways and entered the bone marrow of the skull.

The immune structures located there reacted to antigens coming from the central nervous system, molecules that the immune system is able to recognize as a target. A local reaction occurred earlier than the corresponding signal appeared in more distant lymph nodes.

According to the first author of the work, Jang Hyun Park, such structures had not previously been found in healthy bone marrow. Their location next to the brain may allow the immune system to respond more quickly to changes occurring in it.

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How immune centers reacted to brain cancer

To test whether the found structures are involved in protecting against diseases, the scientists used a mouse model of glioblastoma, an aggressive malignant brain tumor.

The researchers disrupted the work of lymphoid structures in the bone marrow of the skull using a drug. After that, the tumors in the mice grew faster, and the life expectancy of the animals decreased compared to the control group. The results showed that local immune centers not only receive signals from the brain, but also participate in antitumor protection.

The scientists then tried to strengthen this response. A mixture of three immune-stimulating proteins was placed in a gel and applied directly under the scalp of mice. This delivery was designed to increase the production of antibodies in the cranial bone marrow.

The immune response first intensified in the structures inside the bone marrow of the skull and only later appeared in the lymph nodes located outside it. The mice that received the gel rejected tumors more effectively and lived longer than the animals from the control group.

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What is known about similar structures in humans

The researchers also found immune cells in human skull bone marrow samples similar to those found in mice. This indicates the possibility of a similar system in humans, but its structure, functions, and role in protecting against tumors have yet to be confirmed.

Experiments on disruption and enhancement of immune structures were conducted only on mice. Scientists have not tested this treatment method in patients with glioblastoma, so it is not yet possible to talk about its effectiveness or safety for humans.

In the future, the cranial bone marrow may become a new target for local immunotherapy. Theoretically, direct action on the immune centers located next to the brain will enhance the necessary response without affecting the entire immune system of the body.

The authors suggest that the discovery may be important not only for the study of tumors, but also for research on Alzheimer's and Parkinson's diseases, schizophrenia, ovoid syndrome and other conditions with an immune component. So far, these are possible areas of further work, rather than confirmed treatments for these diseases.