Infection and Immunity, August 1999, p. 4161-4170, Vol. 67, No. 8
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Department of Microbiology1 and Department of Medicine,2 The University of Iowa, Iowa City, Iowa, and Department of Medicine, Baylor College of Medicine, Houston, Texas3
Received 14 January 1999/Returned for modification 21 March 1999/Accepted 14 May 1999
Nontypeable Haemophilus influenzae is an exclusive human pathogen which infects the respiratory epithelium. We have initiated studies to explore the interaction of the nontypeable H. influenzae strain 2019 with primary human airway epithelial cells by electron and confocal microscopy. Primary human airway cell cultures were established as monolayers on glass collagen-coated coverslips or on semipermeable membranes at an air-fluid interface. Scanning electron microscopy indicated that bacteria adhered to nonciliated cells in the population. The surface of infected cells showed evidence of cytoskeletal rearrangements manifested by microvilli and lamellipodia extending toward and engaging bacteria. Confocal microscopic analysis demonstrated that infection induced actin polymerization with an increase in cortical actin as well as evidence of actin strands around the bacteria. Transmission electron microscopic analysis showed lamellipodia and microvilli surrounding organisms, as well as organisms adherent to the cell surface. These studies also demonstrated the presence of bacteria within vacuoles inside of airway cells. Confocal microscopic studies with Texas red-labeled dextran (molecular weight, 70,000) indicated that H. influenzae cells were entering cells by the process of macropinocytosis. These studies indicate that nontypeable H. influenzae can initiate cytoskeletal rearrangement within human airway epithelium, resulting in internalization of the bacteria within nonciliated human airway epithelial cells by the process of macropinocytosis.
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