Scientists have discovered that pancreatic cancer attracts regulatory T cells, which suppress the activity of immune cells. In this way, the tumor might escape its destruction by the immune system. The ability to discriminate between friend and foe or between "self" and "foreign" is vital for a functioning immune system. There are numerous protective mechanisms at work to save the body's own tissue from attacks by misguided immune cells. A pivotal role is played by regulatory T cells (Treg cells), which prevent immune reactions against the body's own structures by suppressing the aggressiveness of particular immune cells called T helper cells.