The most abundant defense cells in a typical innate immune response are phagocytes. The most famous of which is the macrophage (likely due to it’s size). Understanding how macrophages operate can build a good theory of how most phagocytes operate.
Where Macrophages Come From
Macrophages start their life as monocytes (much smaller). Monocytes are white bloods cells which are produced in our bone marrow and then go onto circulate through our blood-stream until they are needed.
There are a lot of monocytes in our bodies
It is estimated that at any given time roughly 2 billion monocytes circulate our bodies.
Once they are ready to become macrophages, they cross over into tissue (through the capillaries) and start maturing into macrophages.
How Macrophages Defend
Macrophages have receptors that sense foreign invaders. Once an invader is detected, the macrophage takes up arms and starts moving towards it.
When within range, the macrophage extend itself, attempting to entrap the invader and literally suck it into special compartment (called the phagosome). This compartment is isolated from the rest of the cell and is like a chemical destruction laboratory.
This process is officially referred to as phagocytosis and it forms the basic defense strategy of all phagocytes.
Once the pathogen is inside this compartment, various enzymes are introduced and effectively destroy the entrapped pathogen. After the pathogen has been neutralized, the waste products are safely eliminated from the cell.
In addition to fighting the cell, while the macrophage is active (fighting pathogens) it gives off various chemicals and signals. This attracts other defense cells and is responsible for triggering inflammation.
This section briefly examined how one of the most famous phagocytes (the macrophage) defend our bodies against foreign invaders. The key points include:
- The most abundant defense cells of the innate immune system are phagocyte, while the most famous phagocyte is the macrophage
- Macrophage are large white blood cells that start their life as as much smaller white blood cells produced by the bone marrow called monocytes
- When required, monocytes cross over into the tissue and start maturing into macrophages
- All phagocytes, including macrophages, use a process called phagocytosis to neutralize pathogens
- Phagocytosis involves entrapping the pathogen in a special compartment, using enzymes to destroy it and safely eliminating the waste