THE ATLANTIC - These intercellular messages, ferried about by molecules called interferons, serve as a warning signal to nearby cells—“‘You are about to be infected; it’s time for you to set up an antiviral state,’” says Juliet Morrison, an immunologist at UC Riverside. Recipient cells start battening down the hatches, switching on hundreds of genes that help them pump out suites of defensive proteins. Strong, punchy interferon responses are essential to early viral control, acting as a “first line of defense” that comes online within minutes or hours, says Mario Santiago, an immunologist at the University of Colorado Anschutz Medical Campus. At their best, interferons can contain the infection so quickly that the rest of the immune system hardly needs to get involved.