Diarrhea: Much More than Meets the Eye

On the 4th of July, people are invariably participating in cookouts and picnics eating lots of foods like hot dogs, potato salad, cheeseburgers, and the like while mixing with friends, family, and acquaintances. Invariably someone will get...diarrhea.

Diarrhea is a really meaty subject full of a lot of content that sits at the intersection of many fields. The diarrhea I like best is the kind related to infectious diseases. Infection-incited diarrhea is fascinating for a number of reasons including the role it plays in disseminating a microbe and the role it plays in expelling the microbe from a body desperately trying to eject it. 

A new study was recently published that provides new evidence of the pathogen-clearing role that diarrhea serves. In this study, using mice infection with the bacterium Citrobacter, it was shown that the infection prompts the secretion of the immune system molecule interleukin-22 (IL-22). IL-22, in turn, upregulates the production of a protein called claudin-2. This protein sort of loosens what are usually tight barriers between cells lining the intestine allowing more fluid and salt to make it into the intestinal lumen resulting in diarrhea, which expels the pathogen from the body. In elegant experiments it was shown that mice deficient in claudin-2 experienced worse symptoms suggesting that the IL-22/claudin-2 mechanism is an important component of host defense.

So, when the dreaded rumble presaging the deluge comes realize it's the result of the ingenuity of evolutionary immune mechanisms designed to help (and perhaps embarrass).