White blood cells (also known as leukocytes) play a very important role in our body’s immunity. The movement of cells to damaged and diseased tissue is called leukocyte ‘recruitment’. It is a key step in the inflammatory process.
In our first article we explained how when white blood cells are alerted or activated they become sticky (Sticky Cells and Inflammation). In this article, we explain how sticky cells are enabled to reach body tissue that requires healing.
Leukocyte recruitment is the process whereby white blood cells are alerted to problems in the body and they move out of the blood into the surrounding tissue in order to fight the threats that have been detected. When the process is inhibited or it doesn’t happen, disease and damage go unchecked and our immune system is not doing its job!
It is a carefully controlled and strategic process involving four steps of interaction with the blood vessel wall: Cell rolling adhesion, Activation, Firm adhesion and Transmigration.
In the absence of threats, some leukocytes tether and roll along the vessel wall briefly as part of something called ‘immune surveillance’ (step 1). Invasion of foreign pathogens in the surrounding tissue will send out danger signals into the blood, which will be detected by circulating leukocytes. As a result, cells become activated and “stickier”, leading to step 2, firm adhesion. In order find a way for a leukocyte to cross the vessel wall, the activated cells may crawl (step 3) along the blood vessel surface before finding a gap and squeezing through (step 4. transmigration).
Whether a leukocyte will be recruited is very dependent on the “stickiness” of the cell. The ‘stickier’ a cell is during activation, the more likely it is to stick to the blood vessel wall and transmigrate into the body tissue where it will cause inflammation (in most cases by engulfing and destroying the damaged tissue). There is a direct correlation between leukocyte stickiness and inflammation in the body.
Once the leukocytes have reached their destination, they can begin their work of defending, protecting and repairing. Leukocyte recruitment is a normal and necessary part of immune system function.
Read on for article three:
If white blood cells are the soldiers of our immune system, leukocyte recruitment is the march to war
Leukocyte “stickiness” is required for leukocyte recruitment
The stickier the cells are, the more likely the cells will be recruited and cause inflammation
There is a direct correlation between leukocyte stickiness and inflammation in the body
Leukocyte recruitment is a normal and necessary part of immune system function