Of bugs, bivalves and breathing

Chitin, a tough natural polymer, is an important component of fungal cell walls and the bodies and eggs of parasitic worms, so both plants and mammals have evolved chitin-degrading enzymes known as chitinases to ward off infection.

But chitin is also found in crustacean and clam shells and in insect exoskeletons, making it the second-most abundant biopolymer on Earth. According to Geoffrey L. Chupp, M.D., associate professor of medicine, and colleagues in Paris and Wisconsin, the chitin-related mechanism that protects us from fungi and parasites may also be contributing to a global rise in asthma rates by reacting to shellfish or the chitin-encased dust mites that roam about in our mattresses and carpets.

As reported in the November 15 issue of the New England Journal of Medicine, Chupp’s research group found that levels of YKL-40, a chitinase-like protein, are significantly elevated in patients with severe asthma, defined as those who use rescue inhalers and oral corticosteroids most frequently and require hospitalization for their asthma most often.

Although the study doesn’t prove that YKL-40 is involved in causing asthma, it demonstrates that the protein can be used as a reliable measure of asthma severity.

Jack A. Elias, M.D., chair and Waldemar Von Zedtwitz Professor of Medicine and senior author of the new paper, says the study is among the first to define a parameter for asthma that can be assessed with a blood test.

“This may allow us to identify a subpopulation of patients with severe asthma and give us insights into the biologic processes that make the disease so severe in these individuals," Elias notes. "Our studies also have demonstrated that eliminating YKL–40 decreases specific types of tissue inflammation—which could be of particular benefit to asthmatic patients with an elevated level of this protein.”