Neutrophil extracellular traps are found at epithelial barriers in canine sinonasal aspergillosis

Introduction Sinonasal aspergillosis (SNA) is a frequent cause of chronic nasal discharge, predominantly caused by Aspergillus fumigatus . The infection is typically confined to the nasal cavity and/or frontal sinuses, characterized by superficial mucosal fungal plaques and associated with severe lymphoplasmacytic and neutrophilic inflammation of the mucosa. While Neutrophil Extracellular Traps (NETs) have been demonstrated to restrict fungal hyphal proliferation in animal models, their presence and role in canine SNA remain unexplored. Methods In this study, we quantified the presence of NETs in nasal lavage fluid (NALf) or nasal mucosal biopsies from dogs diagnosed with SNA and healthy controls. To unambiguously detect NETs, we employed three detection techniques. The first method consisted in cell-free DNA detection in NAL. The second method measured myeloperoxidase (MPO)-DNA complexes in NAL by ELISA. The third method aimed to directly identify NETs in nasal biopsies by confocal microscopy and characterize histopathological lesions associated to NETs-enriched areas in corresponding adjacent hematoxylin-eosin tissue sections. Results Interestingly, we were only able to detect NETs in biological samples of dogs with SNA but not in samples from control dogs. Furthermore, NETs-enriched areas were specifically restricted to the surface of the epithelial barrier, where they surrounded fungal spots. Conclusion These results suggest that NETs are involved in the inflammatory response occurring in SNA and likely regulate disease progression. Whether they limit the fungal propagation or contribute to the pathogenesis of the disease remains to be determined, before assessing their role as potential therapeutic target.