User:Immcarle176/Interferon type II

Type II IFN Production
The primary cells that secrete type II IFN are CD4+ T helper 1 (Th1) cells, natural killer (NK) cells, and CD8+ cytotoxic T cells. It can also be secreted by antigen presenting cells (APCs) such as dendritic cells (DCs), macrophages, and B cells to a lesser degree. Type II IFN expression is upregulated by the production of interleukin cytokines, such as IL-12, IL-15, IL-18, as well as type I interferons (IFN-α and IFN-β). Meanwhile, IL-4, IL-10, transforming growth factor-beta (TGF-β) and glucocorticoids are known to downregulate type II IFN expression.

Type II IFN Impact on Cellular Activities
Type II IFN influences the activity of many immune cells. Some of its main functions are to induce IgG isotype switching in B cells; upregulate major histocompatibility complex (MHC) class II expression on APCs; induce CD8+ cytotoxic T cell differention, activation, and proliferation; and activate macrophages. In macrophages, type II IFN stimulates IL-12 expression. IL-12 in turn promotes the secretion of IFN-γ by NK cells and Th1 cells, and it signals naive T helper cells (Th0) to differentiate into Th1 cells.

Type II IFN-mediated signaling
IFN-γ binds to the type II cell-surface receptor, also known as the IFN-gamma receptor (IFNGR) which is part of the class II cytokine receptor family. The IFNGR is composed of two subunits: the IFNGR1 and IFNGR2. IFNGR1 is associated with JAK1 and IFNGR2 is associated with JAK2. Upon IFN-γ binding the receptor, IFNGR1 and IFNGR2 undergo conformational changes that result in the autophosphorylation and activation of JAK1 and JAK2. This leads to a signaling cascade and eventual transcription of target genes. The expression of 236 different genes has been linked to type II IFN-mediated signaling. The proteins expressed by type II IFN-mediated signaling are primarily involved in promoting inflammatory immune responses and regulating other cell-mediated immune responses, such as apoptosis, intracellular IgG trafficking, cytokine signaling and production, hematopoiesis, and cell proliferation and differentiation.

JAK-STAT Pathway
One key pathway triggered by IFN-γ binding IFNGRs is the Janus Kinase and Signal Transducer and Activator of Transcription pathway, more commonly referred to as the JAK-STAT pathway. In the JAK-STAT pathway, activated JAK1 and JAK2 proteins regulate the phosphorylation of tyrosine residues in STAT1 transcription factors. Once STAT1 proteins have been activated, they can come together to form STAT1-STAT1 homodimers. The STAT1-STAT1 homodimers can then enter the cell nucleus due to the amino acid component tyrosine being phosphorylated. They then initiate transcription by binding to gamma interferon activation site (GAS) elements, which are located in the promoter region of interferon stimulated genes (ISGs) that express for antiviral effector proteins, as well as positive and negative regulators of type II IFN signaling pathways.

The JAK proteins also lead to the activation of phosphatidylinositol 3-kinase (PI3K). PI3K leads to the activation of protein kinase C-δ (PKC-δ) which phosphorylates the serine residue in STAT1 transcription factors. The phosphorylation of the serine residues in STAT1-STAT1 homodimers are essential for the full transcription process to occur.

Other Signaling Pathways
Other signaling pathways that are triggered by IFN-γ are the mTOR signaling pathway, the MAPK signaling pathway, and the PI3K/AKT signaling pathway.

Importance in Cancer Immunotherapy
The goal of cancer immunotherapy is to trigger an immune response by the patient's immune cells to attack and kill malignant (cancer-causing) tumor cells. Type II IFN deficiency has been linked to several types of cancer, including B-cell lymphoma and lung cancer. Furthermore, it has been found that in patients receiving the drug durvalumab to treat non-small cell lung carcinoma and transitional cell carcinoma had higher response rates to the drug, and the drug stunted the progression of both types of cancer for a longer duration of time. Thus, promoting the upregulation of type II IFN has been proven to be a crucial part in creating effective cancer immunotherapy treatments.

Involvement in Antitumor Immunity
Type II IFN enhances Th1 cell, cytotoxic T cell, and APC activities, which results in an enhanced immune response against the malignant tumor cells, leading to tumor cell apoptosis and necroptosis (cell death). Furthermore, Type II IFN suppresses the activity of regulatory T cells, which are responsible for silencing immune responses against pathogens, preventing the deactivation of the immune cells involved in the killing of the tumor cells. Type II IFN prevents tumor cell division by directly acting on the tumor cells, which results in increased expression of proteins that inhibit the tumor cells from continuing through the cell cycle (i.e., cell cycle arrest). Type II IFN can also prevent tumor growth by indirectly acting on endothelial cells lining the blood vessels close to the site of the tumor, cutting off blood flow to the tumor cells and thus the supply of necessary resources for tumor cell survival and proliferation.

Barriers
The importance of type II IFN in cancer immunotherapy has been acknowledged; current research is studying the effects of type II IFN on cancer, both as a solo form of treatment and as a form of treatment to be administered alongside other anticancer drugs. But type II IFN has not been approved by the Food and Drug Administration (FDA) to treat cancer, except for malignant osteoporosis. This is most likely due to the fact that while type II IFN is involved in antitumor immunity, some of its functions may enhance the progression of a cancer. When type II IFN acts on tumor cells, it may induce the expression of a transmembrane protein known as programmed death-ligand 1 (PDL1), which allows the tumor cells to evade an attack from immune cells. Type II IFN-mediated signaling may also promote angiogenesis (formation of new blood vessels to the tumor site) and tumor cell proliferation.