Scientists found a hidden "organ" inside the skull

Biologists at Washington University School of Medicine in St. Louis have made an unexpected discovery: previously unknown immune structures are hidden in the skull bones of mice. The scientists believe that a similar "organ" may also exist in humans, helping the immune system recognize and destroy brain tumors. The results of the study have been published in the journal Nature.

The mysterious structures were found in the bone marrow of the mouse skull. In their architecture, they resemble germinal centers — special regions of the lymphatic system where immune B cells undergo a kind of "training" and learn to develop defenses against specific threats.

The path to this discovery was paved by earlier work from the same research group. At that time, the scientists identified tiny channels penetrating the dura mater and connecting brain tissues directly to the skull bones. In the new study, using fluorescent markers, the biologists traced the movement of molecules through these channels — and discovered a direct link between the brain and the immune structures of the bone marrow.

The formations that were found have been named localized lymphoid structures. Their location may prove to be key: the immune cells are situated in immediate proximity to the brain and are capable of responding rapidly to pathological processes within it.

To verify the role of these structures, the scientists conducted a series of experiments on mice with glioma — one of the most aggressive brain tumors. When the activity of the discovered immune formations was suppressed, tumors grew noticeably faster and the animals' lifespan was shortened. Conversely, stimulation of these structures using three immunoactive proteins enhanced the anti-tumor response and significantly improved survival rates in mice.

For now, the scientists cannot state with certainty that an analogous system exists in humans. However, there is already an encouraging sign: follicular T cells were previously found in the bone marrow of the human skull, which may indicate the presence of similar immune structures. If the existence of this mechanism in humans is confirmed, the discovery could provide a fundamentally new approach to treating brain diseases — without direct intervention into brain tissue.