Immune system 'brakes' found
The immune system constantly combats bacteria and viruses
Scientists say they have learnt how the body controls the machinery it uses to fight infections and foreign invaders.
The advance, published in the journal Nature, may one day help find ways to tackle unwanted immune reactions following transplant surgery. The Johns Hopkins University researchers say a protein molecule called carabin may be the body's way of restraining its defences.
The Johns Hopkins team, led by Professor Jun Liu, has been hunting for body chemicals that might shed light on how the immune system is controlled.
They found that a protein called carabin appeared to be important, latching onto microscopic cells active during an infection.
It is made by white blood cells, one of the most important immune system cells.
However, its role actually appears to restrict their ability to mount a response to infection.
They found that when there was more carabin in a cell, it appeared to 'damp down' its activity. Professor Liu said: "It acts like an internal brake to dial down the speed and intensity of an immune response so that it doesn't go too fast or too far, or career out of control and attack healthy cells.