The innate immune system is hard-wired to battle common foes: for instance, the Toll protein in fruit flies specializes in recognizing bacterial and fungal infections. Our own cells contain 10 proteins similar to Toll, called Toll-like receptors, that each recognize distinctive molecules from bacteria and viruses. The one shown here recognizes lipopolysaccharide (shown in red), a molecule found in many bacterial cell walls. When they find these foreign molecules, our Toll-like receptors mobilize an inflammatory response that fights the pathogens. This response is very important: for instance, mice that are deficient in one step of the Toll-like receptor signaling pathway often die of infections from the normal bacteria found in their mouths.
This flyer commemorates the 2011 Nobel Prize in Physiology or Medicine.