Discovery and Contribution of Nontypeable Haemophilus influenzae NTHI1441 to Human Respiratory Epithelial Cell Invasion

Abstract

Nontypeable Haemophilus influenzae (NTHi) is the primary cause of bacterially induced acute exacerbations of chronic obstructive pulmonary disease (COPD). NTHi adheres to and invades host respiratory epithelial cells as a means to persist in the lower airways of adults with COPD. Therefore, we mined the genomes of NTHi strains isolated from the airways of adults with COPD to identify novel proteins to investigate their role in adherence and invasion of human respiratory epithelial cells. An isogenic knockout mutant of the open reading frame NTHI1441 showed a 76.6% ± 5.5% reduction in invasion of human bronchial and alveolar epithelial cells at 1, 3, and 6 h postinfection. Decreased invasion of the NTHI1441 mutant was independent of either intracellular survival or adherence to cells. NTHI1441 is conserved among NTHi genomes. Results of whole-bacterial-cell enzyme-linked immunosorbent assay (ELISA) and flow cytometry experiments identified that NTHI1441 has epitopes expressed on the bacterial cell surface. Adults with COPD develop increased serum IgG against NTHI1441 after experiencing an exacerbation with NTHi. This study reveals NTHI1441 as a novel NTHi virulence factor expressed during infection of the COPD lower airways that contributes to invasion of host respiratory epithelial cells. The role in host cell invasion, conservation among strains, and expression of surface-exposed epitopes suggest that NTHI1441 is a potential target for preventative and therapeutic interventions for disease caused by NTHi.

The intracellular phase of extracellular respiratory tract bacterial pathogens and its role on pathogen-host interactions during infection

“…But also for them an intracellular stage in airway macrophages and epithelial cells is well described [19–21]. For the likewise human-restricted pathogen Haemophilus influenzae, an intracellular stage was found although the ability of the bacterium to replicate intracellularly is still controversial [22,23 ▪ ]. Acinetobacter baumannii and Pseudomonas aeruginosa , both important nosocomial pathogens, were also found to persist within eukaryotic cells in the lung [14,24,25 ▪▪ ,26].…”

“…Information are provided for the Gram-positive cocci S. aureus [17,50,67] and S. pyogenes [18]. Also the Gram-negative bacteria A. baumannii [13,45 ▪▪ ], B. pertussis and B. parapertussis [19,21,68], B. cenocepacia [20], H. influenzae [22,23 ▪ ], and P. aeruginosa [26,69] are described in more detail within this work.…”