Green vegetables have been found to be the source of a chemical signal that is vital for a fully-functioning immune system. Previous research by Marc Veldhoen of The Babraham Institute in Cambridge, England, and colleagues revealed that green vegetables, in particular cruciferous vegetables, contain a compound that can be converted into a molecule that triggers the production of a cell-surface protein called aryl hydrocarbon receptor (AhR). While their latest study has shown that AhR is vital for the correct functioning of immune cells in the gut and the skin known as intra-epithelial lymphocytes (IELs), which act as a first line of defense and play a role in wound repair.  Results showed that mice fed a synthetic diet lacking this key compound experienced a significant reduction in AhR activity and a significant loss of IELs. The loss of IELs resulted in lower levels of antimicrobial proteins, heightened immune activation, and greater susceptibility to injury. "I would have expected cells at the surface would play some role in the interaction with the outside world, but such a clear cut interaction with the diet was unexpected. After feeding otherwise healthy mice a vegetable-poor diet for two to three weeks, I was amazed to see 70 to 80% of these protective cells disappeared," said Veldhoen.