Researchers at the University of California (UC) Davis have shown how the innate immune system distinguishes between dangerous pathogens and friendly microbes. Like burglars entering a house, hostile bacteria give themselves away by breaking into cells. However, sensory proteins instantly detect the invasion, triggering an alarm that mobilizes the innate immune response. This new understanding of immunity could ultimately help researchers find new targets to treat inflammatory disorders. The paper was published online in Nature on March 31, 2013. The immune system has a number of difficult tasks, including differentiating between cells and microbes. However, the body, particularly the digestive tract, contains trillions of beneficial microbes, which must be distinguished from dangerous pathogens. “We are colonized by microbes. In fact, there are more bacteria in the body than cells,” said senior author Dr. Andreas Bäumler, professor and vice chair of research in the UC Davis Department of Medical Microbiogy and Immunology. “The immune system must not overreact to these beneficial microbes. On the other hand, it must react viciously when a pathogen invades.” The key to distinguishing between pathogenic and beneficial bacteria is their differing goals. Ordinary digestive bacteria are content to colonize the gut, while their more virulent cousins must break into cells to survive. Salmonella achieves this by activating enzymes that rearrange the actin in a cell’s cytoskeleton. Fortunately, cellular proteins sense the activating enzymes, leading to a rapid immune response. In the study, the researchers investigated a strain of Salmonella, in both cell lines and animal models, to determine how the innate immune system singles out the bacteria for attack.
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