PavA of Streptococcus pneumoniae modulates adherence, invasion, and meningeal inflammation.

Pneumococcal adherence and virulence factor A (PavA) is displayed to the cell outer surface of Streptococcus pneumoniae and mediates pneumococcal binding to immobilized fibronectin. PavA, which lacks a typical gram-positive signal sequence and cell surface anchorage motif, is essential for pneumococcal virulence in a mouse infection model of septicemia. In this report the impact of PavA on pneumococcal adhesion to and invasion of eukaryotic cells and on experimental pneumococcal meningitis was investigated. In the experimental mouse meningitis model, the virulence of the pavA knockout mutant of S. pneumoniae D39, which did not show alterations of subcellular structures as indicated by electron microscopic studies, was strongly decreased. Pneumococcal strains deficient in PavA showed substantially reduced adherence to and internalization of epithelial cell lines A549 and HEp-2. Similar results were obtained with human brain-derived microvascular endothelial cells and human umbilical vein-derived endothelial cells. Attachment and internalization of pneumococci were not significantly affected by preincubation or cocultivations of pneumococci with anti-PavA antisera. Pneumococcal adherence was also not significantly affected by the addition of PavA protein. Complementation of the pavA knockout strain with exogenously added PavA polypeptide did not restore adherence of the mutant. These data suggest that PavA affects pneumococcal colonization by modulating expression or function of important virulence determinants of S. pneumoniae.

Ectodomains 3 and 4 of human polymeric Immunoglobulin receptor (hpIgR) mediate invasion of Streptococcus pneumoniae into the epithelium.

Streptococcus pneumoniae binds to the ectodomain of the human polymeric Ig receptor (pIgR), also known as secretory component (SC), via a hexapeptide motif in the choline-binding protein SpsA. The SpsA-pIgR interaction mediates adherence and internalization of the human pathogen into epithelial cells. In this study the results of SpsA binding to human, mouse, and chimeric SC strongly supported the human specificity of this unique interaction and suggested that binding sites in the third and fourth Ig-like domain of human SC (D3 and D4, respectively) are involved in SpsA-pIgR complex formation. Binding of SpsA to SC-derived synthetic peptides indicated surface-located potential binding motifs in D3 and D4. Adherence and uptake of pneumococci or SpsA-coated latex beads depended on the SpsA hexapeptide motif as well as SpsA-binding sites in D3 and D4 of human pIgR. The involvement of D3 and D4 in adherence and invasion was demonstrated by the lack of binding of SpsA-coated latex beads to transfected epithelial cells expressing mutated pIgR. Finally, blocking experiments with chimeric human-mouse SC as well as synthetic peptides indicated the participation of D3 and a key role of D4 in pneumococcal invasion.