Scientists at the University of California-San Francisco (UCSF) have discovered that a common compound called chitin triggers an allergic inflammatory response in the lungs of mice.
Chitin is the substance that gives strength and rigidity to the beetle’s back and the crab’s shell and which is also found in insects, moulds and parasitic worms – all common sources of allergies and inflammation.
Humans and other mammals do not produce chitin, but do have specialised enzymes to break it down when it is encountered in the environment.
There are several variants of this anti-chitin enzyme, due to small mutations in the gene that determines its production, and scientists are now investigating the possibility that some of these variants are less effective at breaking down chitin. They are also keen to establish whether individuals with those variants may consequently be more prone to asthma.
One avenue that the UCSF team hope to explore is whether a particular form of asthma which plagues workers in the shellfish industry, 'crab asthma', may be the result of unusually high levels of chitin arising from the large-scale removal and destruction of the hard, chitinous shells of crustaceans.
It is thought that those workers who are most afflicted may have defective forms of the chitin-degrading protein and it is hoped that greater understanding about this might eventually benefit others with asthma who may also have less active versions of the gene for making the anti-chitin enzyme.
In addition to the processes that deals with chitin within the body, this substance is also controlled naturally in the environment by certain bacteria, and it is possible that today's widespread emphasis on hygiene may be contributing to the rise in asthma by removing too many of these microbes.

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First Published in March 2008

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