March 30, 2012

TOO CLEAN: RISE IN ALLERGIES LINKED TO WAR AGAINST BACTERIA.

“Allergic diseases have reached pandemic levels,” begins David Artis’s new paper in Nature Medicine. Artis goes on to say that, while everyone knows allergies are caused by a combination of factors involving both nature and nurture, that knowledge doesn’t help us identify what is culpable—it is not at all clear exactly what is involved, or how the relevant players promote allergic responses.

There is some evidence that one of the causes lies within our guts. Epidemiological studies have linked changes in the species present in commensal bacteria—the trillions of microorganisms that reside in our colon—to the development of allergic diseases. (Typically, somewhere between 1,000 and 15,000 different bacterial species inhabit our guts.) And immunologists know that signaling molecules produced by some immune cells mediate allergic inflammation. . . .

It has been well known for some time that IgE mediates allergies. But no one knew that bacteria living in the gut may use it to check the growth of immune precursor cells in the bone marrow. The finding might have wide ranging implications and help us make sense of other chronic inflammatory disease states that have also been associated with changes in this bacterial populations. Commensal bacteria might impact these other inflammatory conditions—including cancer, infection, and autoimmune disorders—through this mechanism, as well.

Experts have puzzled over the enormous explosion of asthma and allergies in recent years, and been unable to pinpoint the cause. This paper suggests that perhaps the overuse of antibacterial products could be to blame.

It’s a complex world.