Interferon gamma (IFN-γ) is a
dimerized soluble
cytokine
Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrin ...
that is the only member of the type II class of
interferons.
The existence of this interferon, which early in its history was known as immune interferon, was described by E. F. Wheelock as a product of human
leukocytes stimulated with
phytohemagglutinin
Phytohaemagglutinin (PHA, or phytohemagglutinin) is a lectin found in plants, especially certain legumes. PHA actually consists of two closely related proteins, called leucoagglutinin (PHA-L) and PHA-E. These proteins cause blood cells to clump ...
, and by others as a product of antigen-stimulated
lymphocytes.
It was also shown to be produced in human lymphocytes. or
tuberculin
Tuberculin, also known as purified protein derivative, is a combination of proteins that are used in the diagnosis of tuberculosis. This use is referred to as the tuberculin skin test and is recommended only for those at high risk. Reliable admi ...
-sensitized mouse
peritoneal lymphocytes challenged with
Mantoux test
The Mantoux test or Mendel–Mantoux test (also known as the Mantoux screening test, tuberculin sensitivity test, Pirquet test, or PPD test for purified protein derivative) is a tool for screening for tuberculosis (TB) and for tuberculosis diagn ...
(PPD); the resulting
supernatant
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
s were shown to inhibit growth of
vesicular stomatitis virus. Those reports also contained the basic observation underlying the now widely employed
IFN-γ release assay used to test for
tuberculosis
Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, i ...
. In humans, the IFN-γ protein is encoded by the ''IFNG''
gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
.
Through cell signaling, IFN-γ plays a role in regulating the immune response of its target cell.
A key signaling pathway that is activated by type II IFN is the
JAK-STAT signaling pathway
The JAK-STAT signaling pathway is a chain of interactions between proteins in a cell, and is involved in processes such as immunity, cell division, cell death, and tumour formation. The pathway communicates information from chemical signals ou ...
.
IFN-γ plays an important role in both