Characterization of nontypeable Haemophilus influenzae innate interactions with human cells

Abstract: Non-typeable Haemophilus influenzae (NTHi) is a human pathogen causing diseases in the upper and lower respiratory tract. Otitis media-prone children and adults with cystic fibrosis or chronic obstructive pulmonary disease, are repeatedly infected by NTHi Research in recent years brought to light the entry and survival of NTHi in epithelial cells and macrophages. Their internalization could be a means for the bacteria to escape the local immunity or the activity of antibiotics and to persist within the respiratory tract. In the present thesis we have investigated the interactions of NTHi with human cells under nonopsonic conditions. We report that NTHi enters human epithelial and monocytic cells through a receptor-mediated endocytosis that requires microfilament and microtubuli polymerization. The adherence of NTHi to the cells and the subsequent internalization are events highly dependent on beta-glucan receptors on the eukaryotic cell surface. Moreover, the bacterial beta-glucans are pathogen-associated molecular patterns (PAMP) also involved in the NTHi-induced activation of eosinophils. Incubation of eosinophils with either bacteria or a beta-glucn derivative resulted in a time and dose-dependent production of hydrogen peroxide (respiratory burst). Furthermore, the inflammation triggered by NTHi is induced in the presence of lipopolysaccharide-binding protein (LBP), in conjunction with membrane CD14 and toll-like receptor 4 (TLR4). In addition, we show that protein D, expressed on the surface of all H. influenzae strains, contributes to a more efficient binding and entry of NTHi into human monocytes. Finally, we present a new in vitro model system for studying the activity of antibacterial drugs against intracellular NTHi.