Parasite Sensors

How do our organisms know when we are being invaded by parasites? New research shows that rare cells present in our mucosal tissues are critical to trigger the alarm and promote elimination of worms and other parasites. Imagine your body as a huge airplane carrying countless tiny passengers. If you travel a lot, you may already know that some passengers can cause a lot of trouble. Dealing with them requires a system that is able to detect a small disturbance before it becomes a big problem. Luckily, your ‘‘personal airplane’’ is built in with a number of devices to sense and respond to common misbehaving passengers like viruses and bacteria. Now, the good news is that your system has been equipped with the right tools also to avoid complex passengers such as protozoa and worms that try to mess up the flight. Viruses and many types of bacteria express molecules that are unique to them called PAMPs, short for pathogenassociated molecular patterns. They are sensed by pattern recognition receptors expressed by host immune cells, such as Toll-like receptors and NOD-like receptors, triggering the release of inflammatory mediators and engagement of other immune cells that will help to contain or to eliminate the aggressor (Iwasaki and Medzhitov, 2015). The mucosal tissues in particular are points of vulnerability in your ‘‘personal airplane.’’ They are constantly in contact with microbes and parasites that are not part of your helpful microbiota crew. They are also sites of exposure to food, inert particles, and environmental allergens and are under the influence of environmental conditions such as temperature, humidity, oxygen tension in the air, and barometric pressure. Epithelial cells in the mucosa express pattern recognition receptors and are engaged in detection of potential threats. The problem is that most eukaryotic parasites, like protozoa and worms, do not express PAMPs and go unseen by this detection system. How can the host sense and respond to their presence? The answer may lie in a very rare population of intestinal epithelial cells, called tuft cells. They were first described