White blood cells, our body’s first line of defence, blow holes into blood vessels to get the job done. These new findings are published in the journal Cell Reports.
White blood cells, also known as leucocytes, form part of the immune system which groups together tissues protecting the body by fighting against harmful foreign bodies. When you are wounded, or when potentially disease-causing organisms enter your body, these blood cells will move from the blood to the sites of infection and inflammation to get rid of the invaders. Scientists had not been able to figure out how this movement happened. The new research conducted at the Weizmann Institute of Science, though, provides invaluable answers as to how white blood cells reach their targets: by pushing themselves through the walls of blood vessels, leaving behind big holes, as they promptly move to the required location in the body.
Leucocytes are scattered throughout the body, moving in blood and the lymphatic system. When they are signalled of the presence of foreign bodies, they need to get to the infection sites at high speed, and to reach destination, they will actively drill huge ‘cavities’ into the inner endothelial lining of blood vessels to move out. This superpower of leucocytes was witnessed by Professor Ronen Alon and his team. Their analysis was based on a combination of methods involving fluorescence and electron microscopy, in vivo imaging, and a special technique for the blood vessel stimulation in test tubes. The scientists were thus able to identify the immune cells in real time as they were crossing the endothelial cells of blood vessels.
The white blood cells make use of their nuclei to push themselves in between, and into, the endothelium whose cytoskeleton structural filaments are disrupted by this action. This dismantling is what creates the big gaps. The latter are of diameter of several microns.
Previously, the world of science assumed that the endothelial cells would contract like muscles to let the white blood cells squeeze through. However, this is not what was observed by Alon and his team.
“Our study shows that the endothelial cells, which were thought to be dynamic assistants in this process of crossing of blood vessel walls, are really more responders to the ‘physical work’ invested by the white blood cell motors and nuclei in generating gaps and crossing through blood vessels,” explains Alon.
The new study provides great insight not only into the methods of ‘travel’ of immune cells but also in cancer research.
“We believe that small subsets of metastatic tumor cells have the ability to adopt the mechanisms used by immune cells to exit the blood vessels into the lungs, the bone marrow, the brain, and other organs. If this is true, we might be able to identify these subsets and target them before these cells leave their original tumor sites and invade distant organs,” says Prof. Alon.