Neutrophil transendothelial migration in vitro to Streptococcus pneumoniae is pneumolysin dependent

The recruitment of polymorphonuclear leukocytes (PMN) from the vascular space to the alveolar air space is an early event in host defense against pneumococcal pneumonia. Pneumolysin is a virulence factor for Streptococcus pneumoniae, but a specific role for pneumolysin in neutrophil-endothelial cell interactions has not been investigated. Using a Transwell system, we studied in vitro migration of PMNs across a monolayer of human pulmonary microvascular endothelial cells in response to wild-type S. pneumoniae (D39) and a pneumolysin-deficient mutant (plnA−) incubated on the abluminal surface of the monolayer. S. pneumoniae induction of PMN migration was dose dependent and elicited by ≥105 D39. Mutants lacking pneumolysin had dramatically reduced potency for eliciting PMN migration compared with the parent strain (5 × 106 plnA− elicits 18.6% PMN migration vs. 55.5% for 5 × 106 D39). The disparity between D39 and plnA− persisted in ethanol-fixed bacteria, consistent with the properties of pneumolysin. Neithe...