Interferon-β is a member of the type I interferon class. Type I IFNs are involved in the innate immune system, being released non-specifically during the early stage of infection in response to stimuli such as viruses, dsRNA, LPS, and bacterial components. Once secreted by virus-infected or activated cells, they bind to the IFNα/β receptor (IFNAR), which is found on almost all cell types, and, via the JAK-STAT pathway, induce the expression of hundreds of IFN-stimulated genes (ISGs). While the function of many of these proteins remains to be elucidated, a hallmark of type I IFNs is their anti-viral activities, both general and specific against particular viruses. Type I IFNs also regulate cell growth and apoptosis, and exert various immunomodulatory and inflammatory effects. As such, they are also clinically relevant, both as therapeutics and as targets of inhibition for the treatment of various autoimmune diseases and cancer.Mouse IFN-β is a ~20 kD monomeric glycoprotein. It has 50% amino acid sequence homology with mouse IFN-α, its closest related protein, and 62% homology with human IFN-β. IFN-β is currently the therapeutic of choice for treating multiple sclerosis.