Macrophages

Macrophages are immune cells that find and destroy germs, tumor cells and other things that could harm you. They also work as your body’s cleanup crew, help your organs work properly and help maintain homeostasis. Homeostasis is how your body stays in balance. For example, your macrophages balance creating inflammation, which can help fight germs, and reducing inflammation so your healthy tissues aren’t damaged.

Macrophages are the only cells present in every organ of your body. They look for and destroy:

• Viruses, bacteria, fungi or other germs (pathogens)
• Infected cells
• Dead, aging or damaged cells
• Tumor cells
• Bits of cells, or cellular debris
• Inactive or less active synapses (the spaces between nerve cells)

Types

Macrophages have two modes (phenotypes):

• M1, or inflammatory mode: M1 macrophages destroy germs and cancer cells and alert immune cells to infections.
• M2, or anti-inflammatory mode: M2 macrophages help with wound healing, clearing out dead cells and tissue repair.

Macrophages can switch between M1 and M2 modes and can also be somewhere in between.

What do macrophages do?

Macrophages are known for their ability to destroy foreign substances that get into your body. But that’s not all they do. Other macrophage job duties include:

• Activating B cells and T cells, which helps them target pathogens
• Removing dead and damaged cells
• Destroying cancer cells
• Releasing proteins like cytokines that alert other immune cells to infections
• Repairing tissue, healing wounds and reducing inflammation
• Reabsorbing minerals into bones
• Breaking down old red blood cells and recycling the iron
• Regulating fetal tissue development
• Regulating your organ function and maintaining homeostasis

How do they work?

Macrophages have receptors on the outside that they use like antennae. These antennae get signals from substances in the environment around them. These could be signals from chemicals or proteins in your body (like cytokines or opsonins). Or they could be antigens, which are like labels on germs, allergens and cancer cells.

If a macrophage detects something it should get rid of, it swallows or “eats” it (a process called phagocytosis, or “cell eating”). Then, it breaks it apart so your body can get rid of it. Macrophages can also display a germ’s antigen on themselves, so that T cells and B cells can recognize it and become activated.

Signals might also cause macrophages to release chemicals that alert other immune cells to the area, reduce inflammation or help regulate a body process.

Where are macrophages located in your body?

You have macrophages in all tissues in your body. Some are created in your organs as part of fetal development — they’re there when you’re born. Others are created throughout your life, starting out as monocytes in your bone marrow. Monocytes develop into macrophages when they move into your tissues.

Most keep a lookout for and remove germs and damaged cells. But some also have special jobs that help keep your organs working. Examples include:

• Kupffer cells in your liver help repair liver damage and prevent your immune cells from attacking “helpful germs,” like those in your gut microbiome.
• Osteoclasts help repair damaged bone and reabsorb minerals into your bones.
• Microglial cells regulate and repair nerve cells.

What are common conditions associated with macrophages?

Macrophages that aren’t working properly or that cause too much inflammation can lead to:

• Osteoporosis
• Autoimmune disorders, like lupus, rheumatoid arthritis (RA), scleroderma and Type 1 diabetes
• Alcohol-related liver diseases, like alcohol-induced hepatitis
• Cancer
• Cardiovascular disease, like atherosclerosis
• Neurological diseases, like Alzheimer’s disease and multiple sclerosis (MS)
• Macrophage activation syndrome, a complication of rheumatological diseases that causes uncontrolled inflammation

Macrophages also play a role in organ damage due to sepsis.

What is the lifespan of a macrophage?

Macrophage lifespan depends on their locations. Generally, they live for months to years.