BACTERIA might be to blame for many cases of asthma. Researchers in Finland
and the US have found evidence that a bacterial protein can trigger the disease,
while another American study has shown antibiotics can help sufferers.
Everything from pollution to excessive hygiene has been blamed for the
dramatic rise in asthma around the world. But a growing number of studies
suggest that Chlamydia pneumoniae, a common cause of lung infections, is
involved in at least some cases.
There is already evidence that diseases such as atherosclerosis are triggered
by bacteria. One theory is that the bugs鈥� 鈥渉eat shock proteins鈥濃�攚hich
protect cells from various stresses鈥攖rigger an autoimmune reaction against
human heat shock proteins, which are very similar (New 杏吧原创, 31 March, p
18).
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So Maija Leinonen of the National Public Health Institute in Oulu, Finland,
and her colleagues looked for antibodies to C. pneumoniae heat shock protein 60
in blood samples from 24 asthmatics, 17 people with bronchitis and 45 healthy
controls. In the latest issue of the European Respiratory Journal, they report
that asthma sufferers are much more likely to have antibodies to the
protein.
鈥淚t鈥檚 the first time that this protein has been shown to be associated with
asthma,鈥� Leinonen says. Long-term infections may be the problem, she says,
leading to inflammation and asthma attacks.
The findings suggest that antibiotics could help asthma sufferers. Team
member David Hahn of Dean Medical Center in Wisconsin is already enlisting
volunteers for an antibiotic trial. But one such study has recently been
completed. Margaret Kraft of the National Jewish Medical Research Center in
Denver, Colorado, gave 55 asthmatics twice-daily doses of an antibiotic called
clarithromycin for six weeks.
About half the volunteers were infected with C. pneumoniae or another
bacterium called Mycoplasma pneumoniae鈥攁nd these people showed clear
improvements in lung function. 鈥淎s clarithromycin has both antimicrobial and
anti-inflammatory effects, we are evaluating [it] further in hopes of
elucidating the mechanism,鈥� Kraft says.
And antibiotics aren鈥檛 the only option. It might be possible to develop a
vaccine that prevents asthma, Leinonen says. 鈥淚t would be fantastic to have a
vaccine.鈥� Aventis of Canada is already working on a DNA vaccine against C.
pneumoniae, she adds.
It remains to be seen how big a role C. pneumoniae plays. Some studies
suggest it could be involved in as many as half of all cases of asthma in
adults, Hahn says. 鈥淢y personal belief is it鈥檚 greater.鈥�
Margaret Hammerschlag of the State University of New York is sceptical,
however. In unpublished studies, she found the bacterium in only 13 per cent of
asthmatic children, and not at all in adults. 鈥淚t probably does play a role
sometimes,鈥� she says. 鈥淏ut it ain鈥檛 the only player.鈥�