The molecular perspective: interferons.

Abstract

simple and direct. Surgery and radiation attack cancer cells in the most physical manner possible. Most chemotherapeutic drugs are similarly direct, attacking weak spots in cancer cells by blocking the action of a key enzyme or stopping the synthesis of a key protein. The action of interferon, however, occurs at a different level than most of the molecules used in chemotherapy. Interferon is not a toxin designed to poison a key molecule in the cell. Instead, it is a message that is read by human cells. Interferon is one of a growing class of cytokines, proteins that deliver instructions from cell to cell. Normally, interferon, and the similar interleukins, mediate a continual conversation between cells about growth and defenses. Our cells build several different types of interferon (Fig. 1), for discussing different (but overlapping) topics. The largest group is labeled the alpha-interferons, which are made in one form or another by nearly all cells. These interferons, and the similar beta and omega interferons, are used to mobilize our first line of defense against invading organisms, before the immune system has a chance to get started. When a cell gets a signal from these interferons, it builds specialized proteins to fight an infection. For instance, infected cells construct enzymes that degrade the RNA of growing viruses or they hobble the protein synthesis machinery, slowing the construction of viral proteins. In the process, however, these cells also chop up their own messenger RNA and interfere with their normal protein synthesis, slowing growth to a crawl. Gamma-interferon, on the other hand, specializes in a second topic of intercellular conversation. It is made by Tlymphocytes and natural killer cells, delivering messages to other cells in the immune system and telling them to focus on cell-based defenses. Gamma-interferon coaxes cells to build more major histocompatibility complex molecules (Fig. 2) and changes the composition of proteosomes, so that they can display any new anomalous molecules that might be inside. It also activates macrophages and arms them with nitric oxide to help clean up the mess. As with all aspects of the immune system, the picture is not quite as simple as this tidy description might seem. The The Molecular Perspective: Interferons