How flies stay fungus free
Fruit flies use two complementary systems to alert their immune systems to the presence of fungal infections, according to new research from an international team lead by the French National Scientific Research Centre (CNRS). The study is published in the latest edition of the journal Cell. Fungal infections are a problem for insects and mammals alike; over 700 species of fungi are known to attack insects, while in humans fungal infections are particularly a problem in people with weakened immune systems. Understanding how our immune system detects and responds to fungal infections is therefore of crucial importance to medicine. In this latest study, the researchers found that a receptor called GNBP3 is able to bind with glucanes, a type of molecule which is found in the cell walls of fungi. Flies lacking the GNBP3 receptor were particularly susceptible to fungal infections. The researchers also found that an enzyme called Persephone plays a key role in activating the flies' immune system, yet while GNBP3 detects the cell walls of the fungi, Persephone detects the fungi's virulence factors - the chemicals used by the fungi to allow them to invade the host fly and disable its immune system. When a fungus invades an insect, it releases enzymes which digest the insect's carapace and so enable it to get inside the insect. One of these enzymes binds to the precursor of Persephone, activating it and thereby alerting the immune system to the presence of the fungus. 'Our data show that the detection of fungal infections relies on a two-pronged sensor system that constitutes a partially redundant recognition system,' the researchers write. They believe that some fungi may have developed a mechanism to inactivate the GNBP system, which recognises fungus cell walls. This prompted the flies to develop a counterstrategy, based on the recognition of enzymes and other molecules released by the fungus as it attacks the fly. The results lead the researchers to ask whether a similar system exists in mammals.
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