Recurring exposure to soot particles from diesel exhaust reduces the immune system's capacity to fend off infection more persistently than does a one-time exposure to an equivalent amount of particles, tests on rodents indicate.
Inhaling particles less than 2.5 micrometers across is harmful to the heart and lungs. A past study showed that breathing air filled with such emissions for 4 hours temporarily suppressed rats' immune defenses against the bacterium Listeria monocytogenes. Within a week after being deliberately infected with the bacterium, however, the soot-exposed rats cleared the infection as effectively as did animals that hadn't breathed diesel fumes.
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