Interferon type I

Overview
Human type I interferons comprise a vast and growing group of IFN proteins.

All type I IFNs bind to a specific cell surface receptor complex known as the IFN-α receptor (IFNAR) that consists of IFNAR1 and IFNAR2 chains.

Homologous molecules to type I IFNs are found in many species, including most mammals, and some have been identified in birds, reptiles, amphibians and fish species.

Types
The types are designated IFN-α (alpha), IFN-β (beta), IFN-κ (kappa), IFN-δ (delta), IFN-ε (epsilon), IFN-τ (tau), IFN-ω (omega) and IFN-ζ (zeta, also known as limitin).

IFN-α
The IFN-α proteins come in 13 subtypes that are called IFNA1, IFNA2, IFNA4, IFNA5, IFNA6, IFNA7, IFNA8, IFNA10, IFNA13, IFNA14, IFNA16, IFNA17, IFNA21. These genes for these IFN-α molecules are found together in a cluster on chromosome 9.

IFN-β
Two types of IFN-β have been described, IFN-β1 (IFNB1) and IFN-β3 (IFNB3) (a gene designated IFN-β2 is actually IL-6).

IFN-ε, –κ, -τ, and –ζ
IFN-ε, –κ, -τ, and –ζ appear, at this time, to come in a single isoform in humans,.

IFN-ω
IFN-ω, although having only one functional form described to date, has several pseudogenes: , , , , , , and.

Sources and functions
IFN-α and IFN-β are secreted by many cell types including lymphocytes (NK cells, B-cells and T-cells), macrophages, fibroblasts, endothelial cells, osteoblasts and others. They stimulate both macrophages and NK cells to elicit an anti-viral response, and are also active against tumors.

IFN-ω is released by leukocytes at the site of viral infection or tumors.

IFN-α acts as a pyrogenic factor by altering the activity of thermosensitive neurons in the hypothalamus thus causing fever. It does this by binding to opioid receptors and eliciting the release of prostaglandin-E2 (PGE2).

A similar mechanism is used by IFN-α to reduce pain; IFN-α interacts with the μ-opioid receptor to act as an analgesic.