New Orleans, April, 2002
Bus fumes may manipulate natural defences to trigger allergies.
23 April 2002 HELEN PEARSON
A lungful of black diesel fumes is chokingly familiar on city streets. Now scientists have found a way in which these clouds might set off allergies and asthma.
There is evidence linking the rise in airborne diesel particles with the incidence of allergies. Compounds that the sooty specks release in the lungs make the immune system produce chemicals that cause inflammation.
The particles also shut down a second arm of the immune system that is normally fired up by bacterial and viral infection. This converts a normal immune response into an allergic one, Fred Finkelman of the University of Cincinnati and his team told the Experimental Biology 2002 meeting in New Orleans on Monday.
Finkelman suggests that allergies occur through two existing immune pathways - one that deals with certain parasitic worm infections, the other with bacteria and viruses. Allergy results when the first pathway is triggered but the second is not, he proposes.
Thus primed, the immune system overreacts to innocuous proteins in the air, such as on pollen or dust mites. This can result in a streaming nose, wheezing and shortness of breath, owing to the overproduction of mucus and the contraction of airway muscles. "Diesel exhaust makes you more vulnerable," says Finkelman.
"It's one possibility," says Michelle Epstein, who studies allergies at the University of Vienna, Austria, "but there are an enormous number."
Trucks, buses and European cars increasingly use diesel - it's economical and produces less greenhouse gases. But the catalytic converters that remove hydrocarbons from petrol vehicles' exhaust are expensive in diesel motors, so these are rare.
The United States, Japan and many European countries are debating what level of diesel fumes should be allowed. Finkelman says that his finding "supports the argument to reduce the emission of diesel".
Diesel has not been proven to trigger allergies. But it is probably one of many contributors to the rising incidence of allergies in the industrialized world.
"Providing a mechanism strengthens the association," argues Finkelman.
Polluted cites in Eastern Europe and India do not have such a high incidence of allergies. Other components of air pollution, environmental and lifestyle factors are also involved, says Epstein.
Immune signals called cytokines are difficult to measure in body fluids because they break down within minutes. Finkelman's team created stable antibodies that bind to specific cytokines, holding them in tissue fluid long enough to determine their levels.
The scientists exposed mice to diesel particles filtered from an engine exhaust. When subsequently administered with a component of bacterial cell walls, the mice did not show the normal rise in a cytokine called gamma interferon.
Nature News Service
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