Induction ofβ2 Integrin-Dependent Neutrophil Adhesion to Human Alveolar Epithelial Cells by Type 1Streptococcus pneumoniaeand Derived Soluble Factors

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Abstract

Pneumonia caused by Streptococcus pneumoniae is characterized by neutrophil infiltration and variable epithelial injury. Neutrophil adhesion to alveolar epithelial pneumocytes (A549) was measured and demonstrated to be dose-dependent following preincubation of these (A549) pneumocytes with type 1 S. pneumoniae. Adhesion peaked at a bacteria-to-epithelial cell ratio of 5:1 after a 4-h incubation but was absent after 2 h and without FMLP. Filtered conditioned media (CM) from pneumococci cultured with (CM+) or without (CM−) epithelial cells were tested. CM+ induced significant adhesion in the absence of FMLP (P < .001); CM− had no effect. In the presence of FMLP, adhesion induced by both media was significantly greater than by FMLP alone (P < .001) and was significantly blocked (P < .01) by antibodies to CD11b and CD18. CM+ upregulated epithelial intercellular adhesion molecule 1 but CM− did not. These data provide new information concerning the interactions of S. pneumoniae, alveolar epithelial cells, and neutrophils.

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