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 a ...
that is the only member of the type II class of
interferon
Interferons (IFNs, ) are a group of signaling proteins made and released by host cells in response to the presence of several viruses. In a typical scenario, a virus-infected cell will release interferons causing nearby cells to heighten t ...
s.
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
leukocyte
White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mul ...
s stimulated with
phytohemagglutinin, and by others as a product of antigen-stimulated
lymphocytes.
It was also shown to be produced in human lymphocytes. or
tuberculin-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 dia ...
(PPD); the resulting
supernatants 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, in w ...
. 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