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Researchers at St. Jude have gained an important insight into how a certain type of bacterium that commonly infects newborn babies avoids destruction by the immune system and goes on to spread a potentially fatal infection.
The insight came during a study of the role of Group B streptococcus (GBS) bacteria in killing immune cells called macrophages, according to Elisabeth Adderson, MD, Infectious Diseases. A report on this study appears in the May 15 issue of Journal of Infectious Diseases currently posted online.
The finding could help researchers identify new ways to block the spread of GBS in newborns. GBS can infect babies during the delivery process, entering their lungs and setting up an infection that later progresses to meningitis, according to Adderson. Meningitis is an inflammation of the membranes lining the spinal cord and brain and is a potentially fatal disease. Even if macrophages engulf GBS, the battle isn’t over, since these bacteria can use the time inside macrophages to temporarily hide out from the rest of the immune system, Adderson notes.
Many other types of bacteria that become engulfed by macrophages after invading the body trigger the macrophage’s own gene for a molecule called NO. The gene then makes NO, which in turn activates a process called apoptosis, or cell suicide, according to Adderson. Because of the widespread use of this trick by bacteria to kill macrophages; because GBS bacteria themselves use this trick to kill mouse macrophages; and because GBS cause human macrophages to undergo apoptosis, it was logical to suggest that GBS also uses NO to kill human macrophages. The surprising finding made by the St. Jude researchers was that GBS bacteria do not use NO to kill human macrophages.
“We were surprised to discover that GBS fails to trigger this NO reaction in human macrophages,” Adderson said. “This shows that these bacteria use a different trick to kill off macrophages after they’ve used these cells to hide from immune system attack.”
The discovery that GBS use a different pathway to cause apoptosis in human macrophages means that the St. Jude researchers can now turn their attention to finding how these bacteria trigger apoptosis in macrophages. This, in turn, will help the investigators identify new ways to interfere with that devious strategy of GBS and prevent the infection from spreading in newborn babies.
Glen Ulett, a former postdoctoral student at St. Jude, is first author of this paper. Ulett is now at the University of Queensland School of Molecular and Microbial Sciences in Brisbane, Australia.
Last updated: June 2005