Effects on the ciliated epithelium of protein D-producing and -nonproducing nontypeable Haemophilus influenzae in nasopharyngeal tissue cultures

A pair of isogenic, nontypeable Naemophilus influenzae strains, one express ing protein D and the other protein D-negative, was compared in their abili ty to cause damage in a human nasopharyngeal tissue culture model. Damage w as assessed by measuring the ciliary beat frequency (CBF) of tissue specime ns at 12 h intervals. Cultures inoculated with H, influenzae manifested a d ecrease in CBF beginning after 12 h, with a maximum decrease after 36 h, Th e impairment of ciliary function by the protein D-expressing strain was sig nificantly greater than that caused by the protein D-negative mutant (P <.0 1). Tissue specimens examined by scanning and transmission electron microsc opy after 24 h appeared normal. After 48 h of incubation, the protein D-exp ressing strain caused a significant loss of cilia, These findings suggest t hat protein D is involved in the pathogenesis of upper respiratory tract in fections due to nontypeable H, influenzae, probably by enhancing functional and morphological damage to cilia.