Researchers at UT Southwestern Medical Center have identified a protein that is made in the intestinal lining and targets microbial invaders. This offering insights into how the intestine fends off pathogens and maintains friendly relations with symbiotic microbes.
The research team used mice raised inside sterile plastic bubbles. Because they are never in contact with the outer, microbe-filled world, these mice do not have the bacteria that normally colonize the gut. By exposing these "germ-free" mice to different types of gut bacteria, the researchers were able to observe how the epithelial cells lining the intestine reacts to microbial invaders.
They found that when the gut lining comes into contact with bacteria, it produces a protein that binds to sugars that are part of the bacterial outer surfaces. When they bind, the proteins quickly destroy their bacterial targets. Basically, they are killer proteins with a sweet tooth.
The proteien, HIP/PAP, in humans, belongs to a protein class called lectins, which bind to sugar molecules. These particular lectins' seek-and-destroy mission may help to create an "electric fence" that shields the intestinal surface from invading bacteria.
The findings of this study may be offering researchers new clues about the causes of inflammatory bowel disease. Most healthy people have a friendly relationship with their gut microbes, but in patients with inflammatory bowel disease this relationship turns sour and the immune system mounts an attack on the gut's microbial inhabitants that can lead to painful ulcers and bloody diarrhea. Why this happens is not cleat, but the fact that these patients have elevated HIP/PAP production suggests that they are coping with increased numbers of invading intestinal bacteria.