A group of cytokine proteins with antiviral properties, capable of enhancing and modifying the immune response. Interferon is released to coat uninfected cells so that they don't become infected. Some interferons induce antiviral activity, others enhance the immune response.
There are three main classes of interferon: alpha , beta , and gamma .

1. IFNalpha is produced by virus-infected monocytes and lymphocytes .
2. IFNbeta is produced by virus-infected fibroflasts (and some other cell types).
3. IFNgamma is produced by stimulated T and NK cells . IFNgamma increases MHC II expression, activates macrophages , neutrophils and NK cells as well as activating vascular endothelium, promoting T and B cell differentiation and increasing IL1 and IL2 synthesis. Also increases IgG2a and decreases IgE , G1, G2b and G3 (opposite of IL4 ).