The bacterium Streptococcus pneumoniae can be found in the upper airways (the nose, mouth, and throat) of most children. When living in the upper airways, S. pneumoniae is harmless. However, if the bacteria are carried to other sites, they cause disease, for example ear infections and life-threatening pneumonia.
Long-term studies have shown that the upper airways of children do not continuously harbor S. pneumoniae. Rather, it is a cycle of bacterial clearance followed by recolonization, with little known about how the bacteria are cleared.
However, Jeffrey Weiser and colleagues, at the University of Pennsylvania School of Medicine, Philadelphia, have now identified a cellular immune mechanism by which mice clear S. pneumoniae from their upper airways.
In the study, they found that efficient clearance of S. pneumoniae from the upper airways of mice that had not been previously colonized by the bacteria required immune cells known as Th17 cells (CD4+ T cells that secrete the soluble factor IL-17). Further analysis indicated that these cells were required to sustain the recruitment of other immune cells known as monocyte/macrophages, which effectively cleared the pneumococcal bacteria.
The authors suggest these data provide a new model for immune-mediated clearance of S. pneumoniae from the upper airways.
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