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First on the scene
Macrophages, a kind of white blood cell, are the first cells at the scene of infection, and they get there from your blood. Your blood looks like it is just a red fluid but it has lots of other kinds of cells too. There are red blood cells that bring oxygen to every part of your body and white blood cells that fight infections.
Getting to the scene
Infected or damaged cells, like the epithelial cells in our story, call for help by releasing chemicals to attract macrophages. These chemicals also open spaces between blood vessel cells. Macrophages can squeeze between the spaces to get to the action!
When cells call for help
Have you ever had a splinter that after a day or two felt painful, hot, and swollen? Your cells around the splinter were calling for help, and when the blood vessels let macrophages in the infected tissue, they also let some blood fluid seep into the area. This extra fluid and the chemicals released by infected cells can cause inflammation. This hurts, but actually helps your body fight infections better!
Think of macrophages as cell-eating machines. Their name actually means “big eater” in Greek. Macrophages are the biggest type of white blood cells - about 21 micrometers - or 0.00083 inches. Still too small to see with your eyes, but big enough to do the important job of cleaning up unwanted viruses, bacteria, and parts of dead cells.
Macrophages don’t eat cells the same way you might eat your food. Instead, the eating machines engulf viruses and bacteria. This is called phagocytosis. First, the macrophage surrounds the unwanted particle and sucks it in. Then, the macrophage breaks it down by mixing it with enzymes stored in special sacs called lysosomes. The leftover material is then pushed out of the cell as waste.
Macrophages in action
Bringing in more help
Not only do macrophages keep the body clean of debris and invaders, they also call for backup when an infection is too big for them to handle alone. Other immune system cells, like the T-Cells and B-Cells in our story, are alerted that their help is needed by chemicals the macrophages release.
Video from Judith Behnsen on Wikimedia Commons.