What Is the Function of Macrophages?

S. Berger

Macrophages are white blood cells that perform several crucial activities in the immune system. Although the usual function of macrophages is thought to be to promote non-specific, innate immunity, they also help to begin specific defense processes. These cells are vital to the inflammatory response, and can be induced to pursue single targets, such as tumor cells.

Macrophages promote tissue growth and repair following an injury.
Macrophages promote tissue growth and repair following an injury.

In the absence of foreign organisms like bacteria and viruses, one function of macrophages is to devour debris and dead tissue. Macrophages accomplish this task in the same way that they destroy foreign invaders, with a process called phagocytosis. During this process, the macrophage extends pseudopods to grab the object or organism, surrounds it, and takes it into its body inside of a vesicle. A structure called a lysosome then fuses to the vesicle, and destroys the object with enzymes and toxic chemicals.

One function of macrophages is to devour debris and dead tissue.
One function of macrophages is to devour debris and dead tissue.

After phagocytosis has been performed, another function becomes apparent. Molecules on the invader's surface that can be recognized by immune cells, known as antigens, are taken by the macrophage, and bound to a nearby helper T cell in a process known as "presentation." By binding the antigen to a specialized molecule on its own surface, the macrophage ensures that other white blood cells won't mistake it for an invader. If the helper T cell finds a matching antigen to the one it was presented by the macrophage, it will initiate an immune response.

Macrophages are also involved in specific immune responses when recruited by T cells. This macrophage function requires that the T cells release compounds known as lymphokines in response to tumor cells or infected somatic cells. These compounds bind the lymphokine receptors on the macrophage's surface, and activate the macrophage to attack nearby cells.

Another function of macrophages involves the inflammatory response. After tissue has been injured, macrophages in the area will release chemicals that promote blood flow to the region and cause inflammation. The inflammation, although painful, is necessary to ensure that other macrophages and immune cells can arrive to attack potential invaders and clear away dead cells.

Following an injury, a second wave of macrophages arrive about 48 hours later, that are not involved in phagocytosis or inflammation. These macrophages instead release a factor to promote tissue growth, repair, and differentiation in order to help recover from injury-related damage. The exact composition of this factor is not yet known, but tissue injured when deprived of macrophages tends to heal more slowly, providing evidence for its existence.

Phagocytes dispose of cells that have undergone apoptosis, or programmed cell death.
Phagocytes dispose of cells that have undergone apoptosis, or programmed cell death.

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Discussion Comments


@jcraig - Monocytes are actually the white blood cells that can turn into macrophages. Macrophages are not actually made in bone marrow. The marrow produces monocytes which get stored in tissue and then can transform into macrophages or another type of white blood cell depending on needs. I think this would also be how the body knows to create the healing macrophages.

About your second question, I am curious whether HIV/AIDS is related to that problem. I only know the basics, but I'm pretty sure that HIV gets into the body and affect the DNA of cells. Somehow I think it tells the white blood cells not to attack the virus or a lot of other foreign matter that might be in the body. That would be why someone with AIDS getting sick can easily kill them. For anyone who knows more, please add on or feel free to correct me.


I know there are other white blood cells involved in the immune responses. For some reason I seem to remember learning about something called monocytes when I was in biology a long time ago. Does anyone know the function of monocytes and how they interact with the other white blood cells?

Also, I was wondering if there were any conditions in which the macrophages are either unable to recognize foreign bacteria or the opposite when they think that cells in our body are harmful when they are not. I would guess that if either of these happened, it would be devastating and the person could not live long, but what would cause it to happen?


@JimmyT - Just like red blood cells, white blood cells are made in the bone marrow and sent out into the blood stream. I think the purpose of lymph nodes is like you said. The white blood cells drop off bacteria and other waste, and then it is sent through our bodies to be disposed.

This article got me to wonder about how the macrophages know what job they are supposed to be doing. Are there just a certain set of them that are constantly floating around looking for foreign material and another set eating dead cells? My big question is how the macrophages responsible for healing know to be produced, and why the other macrophages can't do the process.


I can't believe there are so many macrophage functions!

I always forget the exact connection, so maybe someone can help me. I know that the white blood cells are connected to the lymph nodes somehow. Are the lymph nodes where the white bloods cells are created, or is it only the place where the unwanted bacteria and invaders are disposed of after they are destroyed? If the lymph nodes don't make white blood cells, where are they made?

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