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To determine the role of pili in mediating adherence of type b and nontypeable Haemophilus influenzae to several respiratory cell types, piliated bacteria, nonpiliated phase variants, and nonpiliated mutants possessing insertionally inactivated pilin genes were tested. Both piliated and nonpiliated strains adhered to HeLa cells, nasal epithelial cells, A549 cells (type II pneumocyte-like cells), and two types of tracheal epithelial cells. Nonpiliated organisms adhered better than piliated variants to cultured HEp-2 cells, whereas piliated organisms adhered better than nonpiliated variants to bronchial epithelial cells and to shed buccal epithelial cells. GM1, a pilus receptor analog, inhibited pilus- but not nonpilus-mediated adherence. Piliated and nonpiliated H. influenzae were equally internalized by A549 cells. Thus, pili mediate adherence to some, but not all, cells derived from human respiratory tissues; nonpilus mechanisms contribute to both adherence, and internalization, of both piliated and nonpiliated organisms.

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