A protein manufactured by the human immune system kills the bacteria that cause tuberculosis, an international team of scientists has observed in laboratory tests. The discovery they say, could lead to new treatments for a disease that affects up to one-third of the world's population. The protein granulysin, made by disease-fighting specialists called killer T cells, destroyed up to 90 per cent of the TB bacteria in lab cultures within three days. The team includes scientists from UCLA, Stanford and four other institutions in the United States and Germany.