Two Yale School of Medicine researchers who study the immune system will share a 2013 Vilcek Prize for their long-standing and influential work on the innate immune system, the body’s first line of defense against infection by bacteria and viruses. The prize went to Richard A. Flavell, Ph.D., chair and Sterling Professor of Immunobiology; and Ruslan M. Medzhitov, Ph.D., the David A. Wallace Professor of Immunobiology.Flavell, a native of England, and his Yale colleagues have discovered several important receptors responsible for innate immunity, and he has made major contributions to our understanding of how activation of the innate immune system triggers the adaptive system’s more specialized immune response. Medzhitov, a native of Tashkent, Uzbekistan, immigrated to the United States in the early 1990s, having been inspired by the then-controversial theories of innate immunity championed by the late Yale immunobiologist Charles A. Janeway Jr., M.D. At the time, innate immunity was deemed unimportant and received scant scientific attention, but by 1997 Medzhitov, Janeway, and colleagues had identified a receptor of the human innate immune system that acts as a pathogen-detecting sentinel and activates adaptive immunity. In the wake of these findings, the study of innate immunity has seen explosive growth, and Medzhitov’s work continues to have significant implications for autoimmune diseases, cancer, and other illnesses.