What Are Activated Macrophages?

Activated macrophages are specialized cells that attack invaders in the body like microorganisms and tumor cells. They work by engulfing targets and digesting them to neutralize them so they cannot continue to produce damage. Along the way, a number of byproducts are released. These can cause tissue inflammation, explaining why the area around a wound often swells and becomes tender as it is healing.

The body produces macrophages from white blood cells. Under normal conditions, macrophages drift through the blood like garbage collectors. They pick up debris, dead cells, and other materials that do not belong to process them. The body recycles any components it finds usable and discards the rest. Free-floating macrophages are also ready to activate in case they are needed, acting as a line of defense in the immune system.

At the site of an injury, white blood cells leak into the area, releasing macrophages that may activate if they receive the right signals. Patients may notice puffiness, white fluid, and redness around the area. These symptoms should decline as the macrophages finish cleaning up and disperse.

In response to certain immune signals or chemicals produced by invading organisms, the macrophages can activate. They become larger and more adept at engulfing foreign objects. Activated macrophages also zero in on materials presenting the same antigens they are sensitized to, which allows them to attack invaders with a high degree of accuracy. Eventually they will become nonfunctional and start to break down, allowing newer cells to replace them.

Historically, the common understanding of activated macrophages was that they were indiscriminate and behaved in the same way. Additional research shows that they can actually develop into a number of different types with their own functions. Each type produces different components and byproducts, and thus behaves uniquely in the body. This information is important for medical treatment, where it may be useful to understand processes going on in the body, as well as the overall understanding of the immune response to disease.

Blood testing can identify activated macrophages in the blood, along with the byproducts they produce when they break down infectious cells and components. Testing may be used to look for infection, inflammation, or other problems in a patient, to provide context for the patient’s reported symptoms. It can also be useful for determining whether a patient is healthy enough for medical procedures, or is responding to treatment for an underlying condition. Sometimes activated macrophages may be present in the blood without any outward sign.