Interferons are a group of signaling proteins made and released by host cells in response to the presence of several pathogens, including viruses, bacteria, and parasites, as well as tumor cells. They belong to the large class of glycoproteins known as cytokines, molecules used for communication between cells to trigger the protective defenses of the immune system that help eradicate pathogens. Interferons are named for their ability to "interfere" with viral replication within host cells. They achieve this by activating immune cells and upregulating the expression of antiviral genes. When interferons are produced in response to a pathogen, they can increase the resistance of neighboring cells to infection, limit the growth of tumors, and boost the efficacy of the immune response.
There are three major types of interferons: Type I, Type II, and Type III, each classified according to their protein structure and the type of receptor through which they signal. Type I interferons, which include IFN-alpha and IFN-beta, are the most widespread and are primarily involved in the immune response to viruses. They are typically produced by infected host cells, including fibroblasts and monocytes. Type II interferon, known primarily as IFN-gamma, is secreted by T lymphocytes and plays a crucial role in modulating the immune system and in defending against bacterial and viral infections. Type III interferons, including IFN-lambda, are involved in the mucosal immunity and are critical for defending against pathogens at mucosal surfaces.
The production and function of interferons are key components of the innate immune system, the body's first line of defense against pathogens. Upon detection of viral RNA or DNA, certain cellular receptors such as TLR (Toll-like receptors) and RLR (RIG-I-like receptors) are activated, leading to a signaling cascade that results in the production of interferons. Once released, interferons bind to specific interferon receptors on the surface of neighboring cells, initiating a signaling pathway that enhances the expression of numerous interferon-stimulated genes (ISGs) that have antiviral properties. These ISGs encode proteins that disrupt various stages of the viral life cycle, from entry into the host cell to replication and assembly.
Interferons also play a significant role in the treatment of several diseases. For example, IFN-alpha is widely used in the treatment of Hepatitis C virus, helping to clear the virus from the body, and in the therapy of certain types of cancer, such as malignant melanoma. However, the use of interferons can be associated with several side effects, such as flu-like symptoms, fatigue, and mood changes, underscoring the need for careful management and monitoring during therapy. Research continues to evolve in the field of interferon therapy, with ongoing studies aimed at improving the efficacy and reducing the side effects of these potent biological response modifiers. The study of interferons remains a dynamic area of medical research, with potential novel therapeutic applications, such as COVID-19 treatment and beyond.