Initial Interactions between Bordetella bronchiseptica and Tracheal Epithelial Cell Cilia

Abstract

The Bordetella genus contain primary colonizing bacteria of the mammalian respiratory tract. Bordetella bind specifically to cilia and colonize the healthy conducting airway epithelium. In this dissertation, I examine the following aspects of initial Bordetella/ciliary binding: 1) the contribution of individual Bordetella virulence factors to binding, 2) the identity of ciliary receptors for Bordetella, and 3) the contribution of airway epithelial innate immune effectors in defense against Bordetella colonization. Bordetella/host cell interactions are modeled using Bordetella bronchiseptica and ciliated rabbit tracheal epithelial cells (RTEC) in a 240 second binding assay. B. bronchiseptica expressing the full complement of virulence factors adhere directly to RTEC cilia. Using single knockout strains of B. bronchiseptica in the ciliary binding assay. I show that the virulence factors filamentous hemagglutinin (FHA), fimbriae, pertactin, and adenylate cyclase-hemolysin (CyaA) contributed to ciliary binding, whereas dermonecrotic toxin, FhaS and the type III secretion system did not. Additional B. bronchiseptica adherence factors exist, as a strain that does not express FHA, fimbriae, pertactin or CyaA retained ciliary binding activity. In an attempt to identify ciliary components for binding, B. bronchiseptica bound cilia with greater affinity following enzymatic removal of terminal sialic acid residues from RTEC cilia. Complementary experiments using the immobilized glycocongugates GM1 and asialoGM1 suggest roles for FHA, and possibly fimbriae and pertactin, in ciliary attachment to asialylated compounds. In attempts to identify airway epithelial innate immune responses that limited ciliary attachment, I show that surfactant protein A (SP-A) blocked B. bronchiseptica adherence to RTEC cilia and nitric oxide (NO) inhibited B. bronchiseptica growth. To determine if B. bronchiseptica might encounter NO during colonization, I developed a novel method to isolate ciliated cells from the tracheal mucosa, and showed constitutive expression of iNOS mRNA in these cells. In summary, I present data that further the understanding of initial Bordetella/ciliary interaction and identify potential pathogen and host targets that may be manipulated to alter Bordetella colonization of the airway.