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What are Macrophages?

How Macrophages Relate to Cancer

Macrophages are specialized white blood cells that attack and consume hostile microbes, cancer cells and cellular debris inside the human body. Their name, derived from Greek, means “big eater;” an apt description of their purpose in the immune system. When activated by T helper cells, macrophages swing into action and envelop bodily threats, disintegrating them and removing the remains. Macrophages are the immune system’s first responders, modifying themselves to counter various threats protecting the body from infection or cancer.

Macrophages take on different names and forms depending on where they function inside the body. For example, macrophages in the liver are called Kupffer cells, while macrophages in the brain and spinal cord are called microglia.

Macrophages begin their life cycle when a T helper cell, another white blood cell subtype, detects a dangerous presence in the body. The T helper cells begin dividing rapidly and emit cytokines which trigger other cells’ transformation into macrophages.  The macrophages leave blood vessels and enter the infected or damaged organ or tissue, adapting itself to be confront whatever threat they find.

Macrophages attack threats through a process called “phagocytosis.” Phagocytosis begins when the macrophage engulfs its target, whether it’s a pathogen, cancer cell or harmful debris. Macrophages seek out other white blood cells called neutrophils which bind to pathogens and act as beacons for the immune system. The macrophage envelops the pathogen, locking it in a pocket called a phagosome. Structures inside the macrophage called lysosomes then combine with the phagosome, using enzymes and peroxides to dissolve it. The macrophage then expels the now-harmless waste material and moves on to its next target.

Macrophages are some of the largest white blood cells in the human immune system, attacking bacteria, viruses, fungi, parasites and more. Beyond addressing current threats, macrophages play an important role in adaptive immunity and the body’s inflammatory response. The macrophage will take a pathogen’s antigen, a protein found on the pathogen’s surface, and integrate it into its own membrane. It also includes molecules indicating to other white blood cells that it isn’t a pathogen itself. When enough macrophages encounter a pathogen and present their antigens, the immune system learns to produce antibodies that help macrophages attack the pathogen.

While macrophages attack tumor cells, their very presence can actually make cancer worse. Macrophage activity can promote chronic inflammation, creating a microenvironment in the body that contributes to cancer growth. The macrophage releases inflammatory compounds activating certain gene switches that stop apoptosis: programmed cell death. Inflamed cells then proliferate out of control, contributing to tumor growth.


  1. Inflammation in Wound Repair: Molecular and Cellular Mechanisms (Eming), 2007
  2. What is a Macrophage? (Mandal)
  3. Macrophage, Ask a Biologist, ASU School of Life Sciences
  4. Macrophages Regulate the Angiogenic Switch in a Mouse Model of Breast Cancer (Lin), 2006
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