IL
Meaning of IL: The numbered vocabulary immune cells use to talk to each other, and the target of a fast growing list of modern drugs.
Definition of IL
IL is the abbreviation for interleukin, any of a large numbered family of small proteins that cells release to signal to one another during an immune response. Each carries an instruction: multiply, mature into a particular type, travel toward an infection, or stop. They are numbered in order of discovery rather than by what they do, so neighboring numbers often have nothing in common.
What does the name mean?
Inter means between, and leukin points to leukocytes, the white blood cells, so the name describes a signal passing between white cells. That was the belief when the family was named, and it is only partly true. Many interleukins are also released by cells with no immune role of their own, including the lining of the gut and airways, connective tissue cells and fat cells. Many act on targets outside the immune system altogether, among them the brain, the bone marrow and the liver.
How does an interleukin differ from a cytokine?
It does not differ in kind. Interleukin is a subgroup inside the wider class of cytokine, the general word for any small protein cells use to signal to each other. The other subgroups carry their own historical names: interferons, named for interfering with viruses, tumor necrosis factors, and chemokines, which direct cell movement. Those divisions record who found what and when, not a real difference in chemistry, and a few molecules sit awkwardly in more than one group.
Why are they such common drug targets?
| Approach | Where it is used |
|---|---|
| Block one interleukin | Persistent inflammation of joints, skin or bowel |
| Block its receptor | The same conditions, from the receiving side |
| Give a manufactured interleukin | Rousing an immune attack on certain cancers |
| Build the signal into a cell therapy | Keeping transferred immune cells alive |
Both directions are in routine use, and that is the point most easily missed. Giving a laboratory-made interleukin to stimulate the immune system against a tumor is only half the story. Far more prescriptions block one instead, because an overactive interleukin signal underlies much long-term inflammatory disease. Severe infection can also drive an uncontrolled surge of these proteins, a state described as a cytokine storm.
Also known as
Used in a sentence
The assay measured IL levels in fluid drawn from the inflamed joint.
Good to know
Interleukins are numbered in the order they were discovered, so the number carries no information about function, and molecules with adjacent numbers may act on entirely different cells for entirely different purposes.