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What is the Difference Between a Cytokine and a Chemokine?
A cytokine and a chemokine are both small proteins made by cells in the immune system. They are important in the production and growth of lymphocytes, and in regulating responses to infection or injury such as inflammation and wound healing. Cytokines are the general category of messenger molecules, while chemokines are a special type of cytokine that direct the migration of white blood cells to infected or damaged tissues. Both use chemical signals to induce changes in other cells, but the latter are specialized to cause cell movement.
Cytokines are a class of proteins secreted in the mammalian immune system, used as messenger molecules to control the duration and strength of the immune response to foreign microorganisms. Many cytokines produced by T cells direct the immune response of various white blood cells (leukocytes) to a foreign microorganism in the body. Among the important varieties are the interleukin (IL) molecules and interferon alpha and beta. The ILs help regulate inflammation, fever, and wound healing, among other things, while the interferons block the replication of viruses.
These proteins heal wounds by signaling blood cells, endothelium, and clotting enzymes to coagulate. There is significant overlap among many cytokines in the healing responses that they facilitate, particularly in response to wounds. They attract various lymphocytes to consume and destroy microorganisms, while guiding skin cells to regrow over the wound, and lead new collagen, blood vessels, and other cells to grow in areas of lost tissue. The various receptors that bind cytokines are called cytokine receptors. Categorizing these receptors has become an important field of research in immunology.
Chemokines are cytokines that induce chemotaxis, which is the movement of a cell or group of cells that follow a chemical messenger to a new location. Unlike cytokines, chemokines have just one major role: to direct the chemotaxis of leukocytes toward foreign, potentially disease-causing microorganims so that these cells are labeled and destroyed by the immune response. Both proteins will act on system target cells, but only chemokines specifically control the chemotaxis of leukocytes during the inflammation that initiates immune response to a pathogen.
Upon binding to receptors on their target, chemokines cause the cells to change their shape and adhere to the endothelial walls inside vessels. Like some other cytokines, they also induce cells to make compounds that kill bacteria, though this is a secondary characteristic of chemokines. Cytokines and chemokines at the site of injury or infection will have similar overall effects: getting different lymphocytes to prevent the increase of bacterial populations.
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![Cytokines and chemokines are both small proteins made by the immune system to attack foreign invaders; both proteins will act on the system target cells, but only chemokines control the chemotaxis of leukocytes.]()
By: Alila Medical MediaCytokines and chemokines are both small proteins made by the immune system to attack foreign invaders; both proteins will act on the system target cells, but only chemokines control the chemotaxis of leukocytes. -
![Cytokines help heal wounds by signaling blood cells, endothelium and clotting enzymes to coagulate, and can be thought of as messenger cells.]()
By: Alila Medical MediaCytokines help heal wounds by signaling blood cells, endothelium and clotting enzymes to coagulate, and can be thought of as messenger cells. -
![Both cytokine and chemokine play a role in wound healing.]()
By: wellphotoBoth cytokine and chemokine play a role in wound healing.
Discussion Comments
It's heartening to read these comments. Cytokines and chemokines certainly are fascinating. I also like the metaphors that have been mentioned. I can't help but think of the immune response as the mobilization of a vast army complete with scouts, messengers, commanders, and, of course, elite soldiers.
@wavy58: There is so much in immunology that remains unknown -- this is what makes it such an exciting part of contemporary biology. Any biologist who says it all makes perfect sense to them is certainly lying! That sense of awe that you speak of is the very thing that draws so many of us into science. Now let's try to get more kids to see how cool this stuff is so that in the future there are still doctors and scientists around!
Chemokines seem to be pretty powerful. They can make cells change shape and move around as ordered.
I never knew I had cytokines and chemokines before reading this article, but I definitely can always tell that something is going on inside my body when I'm sick. I suppose cytokines and inflammation go hand in hand.
I get really weak and nauseated when I have any sort of infection. I feel like my body is under attack, and the exertion of the cytokines and chemokines in the battle against the bad guys really takes a lot out of me.
@Kristee – Yes, it is tragic. My mother-in-law nearly died from sepsis, but it was her body's response to it that made it worse.
The doctor conducted a cytokine assay, and he said that her levels were through the roof. She had to have surgery and be hospitalized for about a month, and he really didn't know whether or not she would survive.
She did recover, but it was a slow process. Her cytokine and chemokine levels are back to normal now, but she still has to take it easy, even one year after the ordeal.
Chemokine and cytokine production can cause a wide range of issues if it is excessive. I've heard of people dying from a cytokine storm. Too many disease-fighting cells were unleashed inside a person's body, and they did more harm than good.
Some people with the bird flu died from having too many cytokines activated at once. Chemokines are not always mentioned, but since they work in conjunction with cytokines, it seems they were also to blame.
I've also heard about people with severe sepsis having an overactive inflammatory response involving cytokines. It's tragic that a person's own body can become their worst enemy while trying to fight off an infection.
The human body is so complex! Even our cells are smart, it seems.
Maybe the science of it all makes perfect sense to a biologist, but I simply stand in awe. Our cytokines and chemokines know how to help heal us, and they also know how to cooperate in order to accomplish this.
I think it's awesome that chemokines are the boss and can tell leukocytes where to go. It's equally awesome that they obey the chemokines! It seems that even in our own bodies, there is a hierarchy, and it works a lot like the employees in an office building.
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