Susceptibility of Human Airway Tissue Models Derived From Different Anatomical Sites to Bordetella pertussis and Its Virulence Factor Adenylate Cyclase Toxin.

Niklas Pallmann,Agmal Scherzad,Stephan Hackenberg,Maria Steinke,Thorsten Walles,David Komla Kessie,Heike Oberwinkler,Rinu Sivarajan

doi:10.3389/fcimb.2021.797491

Abstract

To study the interaction of human pathogens with their host target structures, human tissue models based on primary cells are considered suitable. Complex tissue models of the human airways have been used as infection models for various viral and bacterial pathogens. The Gram-negative bacterium Bordetella pertussis is of relevant clinical interest since whooping cough has developed into a resurgent infectious disease. In the present study, we created three-dimensional tissue models of the human ciliated nasal and tracheo-bronchial mucosa. We compared the innate immune response of these models towards the B. pertussis virulence factor adenylate cyclase toxin (CyaA) and its enzymatically inactive but fully pore-forming toxoid CyaA-AC-. Applying molecular biological, histological, and microbiological assays, we found that 1 µg/ml CyaA elevated the intracellular cAMP level but did not disturb the epithelial barrier integrity of nasal and tracheo-bronchial airway mucosa tissue models. Interestingly, CyaA significantly increased interleukin 6, interleukin 8, and human beta defensin 2 secretion in nasal tissue models, whereas tracheo-bronchial tissue models were not significantly affected compared to the controls. Subsequently, we investigated the interaction of B. pertussis with both differentiated primary nasal and tracheo-bronchial tissue models and demonstrated bacterial adherence and invasion without observing host cell type-specific significant differences. Even though the nasal and the tracheo-bronchial mucosa appear similar from a histological perspective, they are differentially susceptible to B. pertussis CyaA in vitro. Our finding that nasal tissue models showed an increased innate immune response towards the B. pertussis virulence factor CyaA compared to tracheo-bronchial tissue models may reflect the key role of the nasal airway mucosa as the first line of defense against airborne pathogens.

Highlights

The human nasal cavity, the trachea and the bronchi are parts of the conducting airways and are lined by a pseudostratified, ciliated respiratory epithelium
Since B. pertussis targets both the upper and the lower ciliated airways, we further investigated if tissue models based on human nasal epithelial cells (HNEC) and HTEC were susceptible differently to the bacteria and their virulence factor CyaA
In both HNEC- and HTEC-based tissue models, no noticeable inter-donor variance was observed, we found intra-donor variance in nasal models derived from donor N8 (Figure 1B)

Summary

Introduction

The human nasal cavity, the trachea and the bronchi are parts of the conducting airways and are lined by a pseudostratified, ciliated respiratory epithelium. The main cell types of the respiratory epithelium are progenitor-like basal cells, mucusproducing goblet cells and ciliated cells This specialized epithelial layer is an important barrier, e.g. against airborne bacteria. The adenylate cyclase domain of CyaA is delivered to the cytosol where it is activated by cytosolic calmodulin and causes an unregulated conversion of adenosine triphosphate to cyclic adenosine monophosphate (cAMP). This alters the cellular physiology and suppresses the bactericidal function in host cells (Vojtova et al, 2006; Ohnishi et al, 2008; Masin et al, 2015; Angely et al, 2020)

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Conclusion