Implication of proteases and anti-proteases during IAV infection and pulmonary inflammation

Abstract

Introduction Influenza A virus (IAV) is one of the most common infectious pathogens in humans and it causes recurrent epidemics and significant mortality every year. A major pre-requisite for infection by IAV is the cleavage of the hemagglutinin protein (HA) of influenza viruses. It determines the tissue tropism and mediates fusion between viral and endosomal membrane during virus entry into host cells. As the IAV genome does not code for proteases able to cleave HA, cellular host proteases are required to activate HA and have an essential role during infection (1) . However less is known about host proteases able to cleave IAV under natural infection conditions. Therefore, a better understanding of the mechanisms involved in this mechanism, could be important for the understanding of IAV pathogenesis and the development of new therapeutic treatments. The aim of this study is to explore the potential role of the pulmonary host protease human airway trypsin (HAT) (2) and its murine orthologue MAT, during IAV infection and its transcriptional (and post-transcriptional) regulation by different viral and host mediators. Results The experiments were performed in human and murine lung epithelial cells, which were exposed to IAV and to different host cytokines (IL-1β, TNF-α, IFNγ, IFN-α and IL-10). Stimulation during 24h with IAV led to an increase of mRNA expression of HAT in bronchial (BEAS-2B) and alveolar (A549) epithelial human cells and an up-regulation of MAT-1 mRNA in epithelial alveolar murine cells (CMT-2). The addition of the cytokines mentioned above during had no effect on HAT mRNA expression. This results suggest that IAV is an inductor of HAT expression and may ‘subvert’ this host mediator to gain access to lung epithelial cells. Conclusion and future directions As a follow up from these results, the role of HAT will be further examined in vivo and in vitro by using an adenovirus over-expressing HAT (Ad-HAT), available in the laboratory, which allows for efficient over-expression of this protease. If, as expected, we demonstrate further that host proteases have important roles in IAV infection and pathogenesis, the use of anti-proteases will be investigated in vitro and in vivo, using transgenic and adenoviral vectors (Ad-SLPI, Ad-elafin, Ad-alpha-1 proteinase inhibitor), all already available in the laboratory.