Pneumococci are the most common cause of respiratory tract
infections, such as otitis and sinusitis, as well as of severe infections like
pneumonia and meningitis. A new study from Karolinska Institutet in Sweden
published in Nature Microbiology shows how the bacteria can inhibit immune cell
reaction and survive inside cells to give rise to pneumonia.
"This is a paradigm shift that increases our understanding
of how pneumococci cause disease, and might explain the long term consequences
of pneumococcal infections such as for example heart disease," says
Professor Birgitta Henriques-Normark at the Department of Microbiology, Tumour
and Cell Biology, Karolinska Institutet. "This is an important discovery
that will lead to new strategies for tackling pneumococcal infections."
Pneumococci are found in the normal flora of healthy
individuals, and up to 60 percent of pre-school children have the bacteria in
their noses. Usually, these bacteria are harmless but they are also a common
cause of otitis, pneumonia, septicaemia and meningitis. Globally, some two
million people die from pneumococcal infections every year.
To find out why the bacteria only sometimes cause disease, the
researchers looked more closely at the toxin pneumolysin, which is produced by
the pneumococcus. This cytolethal toxin enables pathogenic effects of the
bacteria.
"We made the very surprising discovery of a new property of
pneumolysin," says Professor Henriques-Normark. "We found that
pneumolysin is able to interact with a special receptor, MRC-1, that is found
in certain immune cells, and in so doing trigger an anti-inflammatory
response."
"It has been thought that pneumolysin only induces a
pro-inflammatory response, but we now show that it can also have an
anti-inflammatory role" she continues. "This is because the bacteria
can use pneumolysin as a means to survive the attacks of the immune
system."
The study was conducted on both mouse and human cells, and when
the researchers studied mice lacking the MRC-1 receptor, they observed that
lower numbers of pneumococci were found in the upper respiratory tract. The
researchers believe that the findings may be of importance for development of
treatment and vaccines against pneumococcal infections.
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