Immune cells move through the bloodstream at incredible speeds, yet they manage to stop with remarkable precision to enter damaged tissues and assist the body.
How do they do it? Scientists discovered a braking mechanism that occurs in our bodies, allowing immune T cells to identify exact stop points.
Immune cells are often imagined as smooth spheres, but their surfaces are not smooth at all.
The outer membrane has flexible protrusions, like tiny fingers, which help the cells sense and communicate with their environment.
To cross the blood vessel wall and enter lymph nodes, the “fingers” of T cells attach to special proteins on the vessel wall.
Once attached, the cells roll along until their CCR7 receptors encounter lymph node chemokines, which signal, “Welcome, you have arrived at your target.”
The signal then activates the LFA-1 protein, which binds to sticky molecules on the vessel wall.
This allows the cell to brake sharply, leave the vessel and scan the lymph node for several minutes to hours.
If no foreign agent is found, the T cell returns to circulation.
Thousands of such scans occur every minute in hundreds of lymph nodes to maintain health.
Previous research showed that the braking signal forms on the T cell fingers in less than half a second.
T cells roll about 0.1 millimeters per second, roughly 15 times their diameter comparable to a fighter jet landing.
Unlike a plane with pre-set landing gear, T cells assemble their “braking equipment” on their finger-like protrusions each time they stop.
CCR7 receptors are concentrated at the accessible tips of T cells.
Approximately 5% of LFA-1 molecules are also on these protrusions, along with other molecules required for signaling, allowing the T cell to generate a braking signal in less than half a second.
These findings not only reveal how the immune system operates but also open doors for studying the movement of other cells, including cancer cells that may circulate and stop in new locations to form metastases.
The research could help develop ways to control immune cell movement: for instance, increasing CCR7 receptors on T cells to accelerate their arrival in lymph nodes and improve vaccine efficiency, or restraining harmful immune cells in autoimmune diseases.