Scientists have discovered a previously unknown warning system that contributes to the body's immune system. According to a study published in the journal PNAS, Mitochondria in the white blood cells secrete a web of DNA fibres that raises the alarm. White blood cells are major components of the body's immune defence, and the research group has shown that several types of these cells react against small DNA fragments that are similar to the DNA from bacteria and viruses. The white blood cells spray out a web consisting of mitochondrial DNA (mtDNA) strands. Mitochondria are present in all cells and normally produce the energy needed by the cell, by burning sugar and fat to form water and carbon dioxide. The web that the mitochondria release sends signals to the surrounding cells that the body is under attack, and cause other white blood cells to release a signal substance known as "interferon type 1". This substance helps the immune system to combat the infection. "We show that the white blood cells in the immune system can release mtDNA outside the cells in an active process in response to infectious agents such as bacteria and viruses," said Bjorn Ingelsson, from the Linkoping University in Sweden. "The discovery raises the possibility of further studies in which we will try to reduce the release of mtDNA, and in this way reduce the inflammation that it causes," said Ingelsson. Other types of web formed by white blood cells in the immune system (known as "neutrophils") have been previously known. These cells release meshes coated with antibacterial proteins. However, the formation of the newly discovered mtDNA webs differs fundamentally from that of the other types of web. The researchers have shown that the mtDNA webs are activated within a couple of minutes, which is faster than the neutrophil-based meshes. The latter also lack the signal function that the mtDNA webs have. Further, the mtDNA webs survive in the blood longer before being dissolved. High levels of interferon type 1, the signal substance activated by the mtDNA webs, occur in several autoimmune diseases and several types of cancer. The researchers believe that it may be possible to quantify the secreted mtDNA molecules and interpret the warning signals, and in this way understand these diseases better.