The dominant theory about antibodies is that they directly target and kill disease-causing organisms. In a surprising twist, researchers from the Albert Einstein College of Medicine have discovered that certain antibodies to Streptococcus pneumoniae actually trick the bacteria into killing each other.
Pneumococcal vaccines currently in use today target the pneumococcal capsular polysaccharide (PPS), a sort of armor that surrounds the bacterial cell, protecting it from destruction. Current thought hold that PPS-binding antibodies protect against pneumococcus by inducing opsonic killing, a process in which pathogens are coated with a substance called opsonin, marking the pathogen out for destruction by the immune system.
While such antibodies are an important part of how pneumococcal vaccines protect against disease, there are PPS-specific antibodies that do not promote opsonic killing but are protective nonetheless.
In the study, Masahide Yano and his colleagues identify one of mechanisms these non-opsonic antibodies use. They increase the rate of communication between the bacterial cells as well as competence-induced killing, or fratricide, where the bacteria naturally kill each other off because of overconcentration.
"These findings reveal a novel, previously unsuspected mechanism by which certain PPS-specific antibodies exert a direct effect on pneumococcal biology that has broad implications for bacterial clearance, genetic exchange and antibody immunity to pneumococcus," says Yano.
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More information: Antibodies to Streptococcus pneumoniae Capsular Polysaccharide Enhance Pneumococcal Quorum Sensing, 13 September 2011 mBio vol. 2 no. 5 e00176-11. doi: 10.1128/mBio.00176-11