Macrophage

Function

Amacrophageis a large white blood cell that is an important part of our immune system. The word 'macrophage' literally means 'big eater.' Its job is to clean our body of microscopic debris and invaders. A macrophage has the ability to locate and 'eat' particles such as bacteria, viruses, fungi, and parasites.

The macrophage accomplishes its ongoing cleanup task by engulfing unwanted particles and 'eating' them. A macrophage uses a process called phagocytosis to destroy and get rid of unwanted particles in the body.Phagocytosisliterally means 'eat cell.' The process works like this: as the macrophage engulfs the particle, a pocket called a phagosome is formed around it. Then, enzymes are released into the phagosome by an organelle within the macrophage called a lysosome. Much like the enzymes in our own stomach are released to digest our food, the enzymes released by the lysosome digest and break up the particle. The remaining debris, or what is left of the particle, exits the macrophage to be absorbed back into the body.

Another fascinating aspect of a macrophage is its ability to know which cells to destroy and which ones to leave alone. Healthy, living cells within our body have a particular set of proteins on their outer membrane. They are essentially ID tags for our cells. If the cell is displaying an incorrect ID tag, the white blood cell destroys it. This is how our immune system recognizes our own cells versus foreign bodies.

Although macrophages do not distinguish between the different types of bacteria, viruses, or other outsiders, they do recognize that those particles do not belong in the body by detecting the different outer proteins. Macrophages even have the ability to detect signals sent out by bacteria (like sharks and the smell of blood), allowing them to travel to the site of infection. Then, once they have engulfed the invader and started to digest it, they are able to take a part of the invader called an ‘antigen’ and present it on the outside of their cell membrane. They present the antigen using special proteins in their cell membrane. When it meets up with another immune cell it announces which pathogen it is (bacteria, virus, etc.).This helps the other cells in your immune system launch an immune response.

Structure

Macrophages are relative large white blood cells, so they have a large surface area of membrane. The membrane is formed into many pseudopods – extensions of cell that can grab and surround smaller cells. While they are large, they are also flexible and can move through tissues and organs easily. Macrophages contain a large number of lysosomes. Their cell membrane includes many special proteins for receiving chemical messages and presenting antigens.

Structure-Function Connection:

  1. Why do you think it would be beneficial for macrophages to be large and have a large surface area of membrane with psuedopods?
  1. Why might it be beneficial for macrophages to contain a lot of lysosomes?
  1. Why do you think macrophages have special proteins on the outside of their cell membranes?