Pneumococcus identified as potential protectant against secondary infection with flu
Numerous studies have shown that severe illness and death may result if an individual develops a secondary respiratory infection after developing the flu, but the researchers found that a bacterial protein pneumolysin could protect immune cells in the lungs, according to a Wistar Institute press release.
The findings-published in the August issue of the journal Virology-were based on a study of influenza infection in mice.
According to Jan Erikson, a professor at The Wistar Institute, a cancer research and vaccine development center, the team examined how pre-colonization of the bacteria in the respiratory system could affect a subsequent flu infection.
"Our studies showed that prior colonization offered a protective effect against severe disease in mice, and we were able to point to the bacterial virulence factor pneumolysin in mediating this protection," Erikson said.
The study found that mice that were colonized by pneumococci 10 days before exposure to the flu were much less likely to develop severe secondary infections or pneumonia than mice who were not colonized by the bacteria.
In mice that were exposed to the flu virus first before being exposed to pneumococci, disease symptoms were exacerbated after the secondary infection.
"Mice that were first exposed to pneumococci exhibited less inflammation in the lungs following influenza infection," Erikson said. "Virus infection wasn't blocked but the response to it was changed such that the mice no longer showed signs of illness."
Using mutant strains of the bacteria that lacked certain proteins, Erikson and the team of researchers were able to identify one protein-pneumolysin-that was necessary to generate the combative effect of pneumococcus. The findings showed alveolar macrophages, a type of immune cell in the lungs, were less likely to call inflammation-causing cells to the lungs in the presence of the bacteria.
"It remains to be seen what lessons we can learn from pneumococcus in lessening flu infections, but I would be interested in seeing if we could get the benefit of pneumococcal colonization without the associated risks," Erikson said.