This is interesting. I recall reading articles not long ago that talked about a treatment for crone’s disease (an autoimmune disease that affects the bowel), that included giving a person pig worms–a parasite much like those that naturally attack human beings, but will automatically die after a while (since we aren’t their natural habitat). The thing is, the doctors/scientists believe that Crone’s and possibly other autoimmune diseases could be caused by an immune system having nothing there to attack but itself. So, ironically, while cleanliness is important at combating certain diseases, it seems that too much of a good thing can be bad. As my Dad used to tell me when I was a kid, “a little dirt is good for you!”
William Parker is an assistant professor of experimental surgery at Duke Medical Center. Over the past few years he has been collecting wild rats not far from his office in Durham, North Carolina. Duke Medical Center is a serious, high-profile sort of place, and collecting wild rats is, at this point in history, just a wee bit taboo. But Parker went out and found rat colonies, living among boxes and urban realities. He gave them food, to get them used to taking food and then, slowly, he put out traps. He could be seen for a while, moving along darkened streets, carrying his quarry — their bald tails dangling — one in each arm. He took them back to the lab and there, among the civilized, domesticated, rats, studied them. He examined their immune systems. He predicted that the wild rats, because they are exposed to a slew of parasites (like our wild ancestors), would have fewer problems associated with autoimmune diseases and that they would be, despite their plagues of pathogens, more healthy. The lab rats, Parker hypothesized, like us, had immune systems with “basically nothing to do.” The wild rats had immune systems primed by and focused on the worms of the wild world.
Parker has begun comparing wild and lab rat immune systems and it is clear they are different. Some antibodies, particularly IgE, are far more abundant in wild rats than in lab rats. A separate study has shown the same is true in the comparison between wolves and domestic dogs. One’s first reaction to noticing that the immune systems of lab rats behave differently from those of wild (and natural) rats might be to say that we should stop studying lab rats. Domestication has rendered them strange and no longer representative of a wild mammal. Fortunately, our own lifestyles have rendered us strange, too. The “strange” response of the lab rats more closely resembles that of our immune system than do the wilder responses of wild rats, wolves, or for that matter any of the other mammals that have been studied to date.
The lives of lab rats and wild rats differ in many ways, and so there are many factors that might explain the differences in their immune systems. But the feature that stands out most is that lab rats have no parasites and, for quite a few generations, no history of parasites. In addition (and here both I and the researchers themselves struggle to find the right words), the wild rat immune system seems more “balanced” than that of the lab rats. Anecdotally, it appears as though mammal immune systems are tuned up with parasites in mind. When parasites are absent, the tuning is wrong. The immunological orchestra is too far off-key, far enough in fact that it attacks pollen (hence allergies) and even the body itself (in the case of autoimmune diseases).