Pollens destroy respiratory epithelial cell anchors and drive alphaherpesvirus infection

Jolien Van Cleemput,Francis Impens,Kris Gevaert,Hans J Nauwynck,Kathlyn Laval,Katrien C K Poelaert,Wim Van Den Broeck

doi:10.1038/s41598-019-41305-y

Abstract

Pollens are well-known triggers of respiratory allergies and asthma. The pollen burden in today’s ambient air is constantly increasing due to rising climate change and air pollution. How pollens interact with the respiratory mucosa remains largely unknown due to a lack of representative model systems. We here demonstrate how pollen proteases of Kentucky bluegrass, white birch and hazel selectively destroy integrity and anchorage of columnar respiratory epithelial cells, but not of basal cells, in both ex vivo respiratory mucosal explants and in vitro primary equine respiratory epithelial cells (EREC). In turn, this pollen protease-induced damage to respiratory epithelial cell anchorage resulted in increased infection by the host-specific and ancestral alphaherpesvirus equine herpesvirus type 1 (EHV1). Pollen proteases of all three plant species were characterized by zymography and those of white birch were fully identified for the first time as serine proteases of the subtilase family and meiotic prophase aminopeptidase 1 using mass spectrometry-based proteomics. Together, our findings demonstrate that pollen proteases selectively and irreversibly damage integrity and anchorage of columnar respiratory epithelial cells. In turn, alphaherpesviruses benefit from this partial loss-of-barrier function, resulting in increased infection of the respiratory epithelium.

Highlights

Asthma and seasonal rhinitis are two allergic diseases with increasing morbidities worldwide[1,2]
The epithelial barrier is normally preserved by firm intercellular junctions (ICJ), which create a network of close connections between adjacent cells and maintain epithelial integrity
All of these substances are potentially involved in the initiation or progression of allergic diseases, but pollens are among the gold standards[3,35,36,37]

Summary

Introduction

Asthma and seasonal rhinitis are two allergic diseases with increasing morbidities worldwide[1,2]. The delivery of pollen allergens to sub-epithelial antigen presenting cells initiates the priming of T helper 2 (Th2) cells, a key step in the immunopathology of allergy[8] This hypothesis is based on previous studies showing that pollen proteases are able to disrupt epithelial integrity in continuous cell lines[6,7,9]. A more recent study using better representative primary isolated human bronchial epithelial cells showed that the epithelial barrier is not disrupted upon treatment with pollen diffusates[10]. The discrepancy between these studies could be explained by the model systems used. Pollen-induced effects and host-specific alphaherpesvirus infections can optimally be studied using representative equine ex vivo and in vitro models, known to mimic in vivo conditions[12,16]

Methods

Results

Conclusion