Mast cells are part of the body’s immune system, residing in connective tissue and releasing compounds during allergic reaction or in response to injury or inflammation. They are found throughout the body, particularly at sites where pathogens can gain access, such as the gastrointestinal tract and the skin. As one of the first inflammatory cells to encounter an invading pathogen, they play a critical role in innate immunity and defense. Guntram Grassl is examining the role of mast cells in Salmonella infections to increase understanding of how these bacteria interact with host cells and how these interactions result in disease. He is determining how mast cells are activated in response to Salmonella and characterizing which factors mediate these effects. He is also studying how infections progress in the absence of mast cells. An increased understanding of how Salmonella causes disease may ultimately lead to the development of new ways to boost the innate immune response against bacterial infections and may lead to the development of new drugs that interfere with the way pathogens trigger disease.