Swine Song

Some parasites and pathogens suppress inflammation and we may learn from them how to block the cycle of conflagration fundamental to many diseases.

“My bowels are alive with the swine Trichuris!”

This may not be a common refrain yet, but it may signal the success of new treatments for destructive inflammation of the intestines, e.g. inflammatory bowel disease, Crohn’s disease and perhaps even Celiac. In these diseases the intestines continue to rachet-up their immune defenses in response to common gut bacteria, food or self-antigens. These inflammatory diseases don’t occur in developing countries with compromised water and sewage systems, and with their related parasites and chronic infectious diseases. This correspondence of diminished exposure to parasites and pathogens, with increased occurrence of inflammatory diseases is the basis for the hygiene hypothesis that associates lack of childhood exposure to subsequent chronic diseases.

Trichuris is a genus of whipworms that live in the large bowel of mammals. These parasites attach to the lining of the bowel and release eggs that carry the infection to other individuals. Different species of Trichuris are adapted to each host species, so that eggs of the swine whipworm will produce only a transient infestation in humans. Consistent with the hygiene hypothesis, people given swine whipworm eggs only temporarily harbor the parasites, but this exposure to the parasite also provides relief from patients with Crohn’s disease.

The intestines are a major organ of the immune system. They are home to most of the lymphocytes and developmentally most of the immune organs start as branches of the digestive tract. The intestines must distinguish between food, friendly microbes and pathogens. Simplistically, that means that it must declare friend or foe, self or non-self, for each molecule, generally protein or carbohydrate, that is presented on its surface. Inflammation causes an alarming shift in the threshold toward foe and in the throes of intense inflammation, many mistakes are made and friendly cells are sacrificed. This is inflammatory bowel disease.

Parasites living in the bowels are adapted to suppress inflammation and thus, it is not surprising that infesting inflamed bowels with parasites might result in a spillover of the suppression into pathologically inflamed tissue. This may even be transmitted to the whole patient. It would make sense that whipworm treatments would benefit a variety of inflammatory diseases including allergies/asthma, arthritis and perhaps some cancers. Generalized suppression of inflammation may even have an impact on heart disease and autoimmune diseases such as MS, Alzheimer’s and diabetes.

There is no opposite to inflammation. There is only the absence of inflammation or anti-inflammation. Perhaps a closer approximation of the opposite would be tolerance. The healthy intestine does not react to itself, i.e. it is self-tolerant, because cells of the immune system that had the ability to recognize and bind to self molecules were killed early in their development (clonal deletion.) Food is a different problem, because it is not present as the lymphocytes develop. The intestine has an active system to suppress immune action against components of food and beneficial bacteria of the gut. In the absence of inflammation, the intestines teach tolerance that spreads throughout the body. Whipworms (and some bacteria) evoke a tolerant state in bowels by suppressing inflammation and researchers are actively trying to figure out how they do it.