title: Cellular interaction of nontypeable Haemophilus influenzae triggers cytotoxicity of infected type II alveolar cells via apoptosis.
abstract: Nontypeable Haemophilus influenzae (NTHi) is an important cause of lower respiratory tract infections, resulting in exacerbations of chronic obstructive pulmonary disease (COPD). Despite its pathogenic potential, little is known regarding the role of intracellular NTHi in pathogenesis of pulmonary infection. Kinetics of NTHi internalization was studied using gentamicin protection assays. NTHi strains isolated from COPD patients efficiently adhere to and invade type II alveolar (A549) cells. During early stages, that is, 6 h postinfection, we noted a substantial increase in NTHi invasion with no evidence of intracellular replication. Electron microscopy revealed that the majority of internalized NTHi resided within membrane bound acidic endocytic vacuoles. However, at later stages, that is, 8 h postinfection, significant reduction in viable intracellular NTHi was observed and vacuoles were found to be empty with NTHi escape into the cytosol. By 12 h, cytopathic changes of cells were evident with massive vacuolization of cytoplasm, intense chromatin condensation, and intact plasma membrane. Furthermore, analysis of apoptotic markers confirmed that infected A549 cells underwent apoptosis at later stages. In addition, inhibition of internalization of NTHi by cytochalasin D prevented apoptosis of cells. Collectively, these findings suggest that internalization of NTHi and its escape from vacuolar compartments triggers cytotoxicity of alveolar cells via apoptosis during the infection process.
authors.affiliation: Department of Experimental Medicine and Biotechnology, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India Department of Pediatrics, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India.
authors.forename: Manu
authors.initials: M
authors.lastname: Goyal
authors.affiliation: Department of Pediatrics, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India.
authors.forename: Meenu
authors.initials: M
authors.lastname: Singh
authors.affiliation: Department of Medical Microbiology, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India.
authors.forename: Pallab
authors.initials: P
authors.lastname: Ray
authors.affiliation: Department of Cytology and Gynaecological Pathology, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India.
authors.forename: Radhika
authors.initials: R
authors.lastname: Srinivasan
authors.affiliation: Department of Experimental Medicine and Biotechnology, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India superoxide@sify.com.
authors.forename: Anuradha
authors.initials: A
authors.lastname: Chakraborti
mesh_terms: D017209:Apoptosis; D015373:Bacterial Typing Techniques; D002460:Cell Line; D003600:Cytosol / Q000382:microbiology; D004705:Endocytosis; D004847:Epithelial Cells / Q000382:microbiology* / Q000502:physiology*; D006193:Haemophilus influenzae / Q000145:classification / Q000502:physiology*; D054884:Host-Pathogen Interactions; D006801:Humans; D046529:Microscopy, Electron, Transmission; D013997:Time Factors; D014617:Vacuoles / Q000382:microbiology
keywords: NTHi; cell death; host cells; internalization