Lymphotoxin is a cytokine, or intercellular messenger, and plays an important role in the immunological balance of the gastrointestinal tract. It regulates the immune system of the digestive tract, which is made up of immune cells, immunoglobulins (antibodies) as well as intestinal bacteria. An international team of scientists has now discovered how this complex interaction functions and how lymphotoxin controls the production of immunoglobulins in the gut.