- Interferons are a family of broad-spectrum immunoregulatory and antiviral agents. They were first recognized by the phenomenon of viral interference, where the animals infected with one virus became resistant to the infection by a second unrelated virus.
- These are signalling proteins.
According to their functions, three main types of interferons are determined.
Interferons of I type include the major families of α-interferons (IFN-α) and β-interferons (IFN-β), as well as several minor interferon groups (e.g., omega-interferon).
α-Interferon is produced by leukocytes, while fibroblasts and probably other cell types synthesize β-interferon.
- Cells start to express alpha- or beta-interferons being infected by a virus. Interferons arise in the extracellular fluid and bind to the specific receptors on the membranes of uninfected neighbouring cells.
- The bound interferon renders its antiviral effect. Several cellular genes are found to derepress under α- and β-interferon activities allowing the synthesis of novel enzymes. One of them, a protein kinase, catalyzes the phosphorylation of initiation factor and ribosomal proteins necessary for protein synthesis, thereby reducing greatly the viral mRNA translation.
- Another enzyme, oligoadenylate synthase, accelerates the formation of a short polymer of adenylic acid, which activates a latent endonuclease (RNAse L) that in turn degrades both viral and host mRNA.
Interferon of type II is known as γ-interferon (IFN-γ).
- It differs strongly from two above-mentioned interferons, exhibiting the traits of typical interleukin. Gamma-interferon is produced by T helper cells of 1 type; it stimulates different cell populations especially macrophages, NK cells, supports conversion of “naive” Th0-cells into Th1 type, thus maintaining cell-mediated inflammation.
- Also, it enhances the expression of HLA antigens on the cell surface.
Interferons of type III include three lambda interferons (IFN-λ) as well as some other regulatory molecules. They demonstrate evident antiviral activity.
- The interferons are proven to have a broad scope of actions beyond the control of viral infection.
- It is clear, for example, those interferon-induced enzymes may inhibit host cell division together with the blockade of viral replication.
- The interferons may also modulate the activity of other immune cells, e.g. natural killer cells.