interferon

Any of several related proteins produced by all vertebrates and possibly some invertebrates. They play an important role in resistance to infection. The body's most rapidly produced and important defense against viruses, they can also combat bacteria and parasites (see parasitism), inhibit cell division, and promote or impede cell differentiation. Interferon's effect is indirect—it reacts with susceptible cells, which then resist virus multiplication—in contrast to antibodies, which act by combining directly with a specific virus. Various types of interferons are distinguished by their characteristics as proteins and by which cells produce them. Some are now produced by genetic engineering. Initial hopes that interferon would be a wonder drug for a wide variety of diseases were deflated by its serious side effects, but a few rare conditions respond to it.