Sydney, Feb 27 : Australian researchers have discovered how a protein works to boost the body's natural-killing immune cells -- a type of white blood cell which hunts and destroys foreign cells in the body, including tumours, breast and colon cancer and melanoma cells. The protein called "ID2" works as a switch that can also be manipulated to fight viral infections or to help patients whose immune systems have not developed properly because their bodies lack natural killer cells. It works by allowing natural killer cells to become responsive to growth factors in the blood, called "Interleukin -15 (IL-15)" that keep the natural killer cells active and alive. Using the growth factor, IL-15, the immune deficiencies in cells can be conquered by 'tricking' the immune cells into becoming natural killer cells, the researchers explained. "The real paradigm shift is that we can now make natural killer cells appear even when this switch is missing, purely by supplying more growth factor to the specific environment -- we can push cells to become natural killer cells. It's a really novel biological discovery," said lead researcher Nick Huntington from Walter and Eliza Hall Institute in Australia. The study, published in the journal Immunity, noted that researchers have now discovered how to best keep these natural killer cells fit and healthy to boost their activity or numbers or survival in the body in order to fight against cancer. Conversely, the natural killer cell switch could also potentially be turned off in instances in which these cells proved damaging, such as when they prompt the rejection of donor stem cells in bone marrow transplants or produce signals that result in the potentially fatal toxic shock syndrome.