The polymeric immunoglobulin receptor translocates pneumococci across human nasopharyngeal epithelial cells

The polymeric immunoglobulin receptor (plgR) plays a crucial role in mucosal immunity against microbial infection by transporting polymeric immunoglobulins (plg) across the mucosal epithelium. We report here that the human plgR (hplgR) can bind to a major pneumococcal adhesin, CbpA. Expression of hplgR in human nasopharyngeal cells and MDCK cells greatly enhanced pneumococcal adherence and invasion. The hplgR-mediated bacterial adherence and invasion were abolished by either insertional knockout of cbpA or antibodies against either hplgR or CbpA. In contrast, rabbit plgR (rplgR) did not bind to CbpA and its expression in MDCK cells did not enhance pneumococcal adherence and invasion. These results suggest that pneumococci are a novel example of a pathogen co-opting the pig transcytosis machinery to promote translocation across a mucosal barrier.