Structural and functional changes of the duodenum in human norovirus infection

Background: Norovirus infection is the most frequent cause of infectious diarrhoea in the western world. This study aimed to characterise functionally and histomorphologically the diseased duodenum in human biopsies. Methods: Norovirus infection was diagnosed by the Kaplan criteria and confirmed by PCR of stool samples. Duodenal biopsies were obtained endoscopically. In miniaturised Ussing chambers, short circuit current, flux measurements and impedance spectroscopy were performed. Histological analysis including apoptosis staining and characterisation of intraepithelial lymphocytes was performed. Tight junction proteins were quantified by immunoblotting. Results: In norovirus infection, epithelial resistance decreased from (mean (SEM)) 24 (2) Ω cm2 in controls to 10 (1) Ω cm2. Mannitol flux increased from 113 (24) nmol h−1 cm−2 in controls to 242 (29) nmol h−1 cm−2. Microdissection revealed a villus surface area reduced by 47% (6.6%). Intraepithelial lymphocytes were increased to 63 (7) per 100 enterocytes, with an increased rate of perforin-positive cytotoxic T cells. Expression of tight junctional proteins occludin, claudin-4 and claudin-5 was reduced. The epithelial apoptotic ratio was doubled in norovirus infection. Furthermore, the basal short circuit current was increased in norovirus infection and could be reduced by bumetanide and 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB). Conclusions: Norovirus infection leads to epithelial barrier dysfunction paralleled by a reduction of sealing tight junctional proteins and an increase in epithelial apoptosis, which may partly be mediated by increased cytotoxic intraepithelial lymphocytes. Furthermore, active anion secretion is markedly stimulated. Thus, the diarrhoea in norovirus infection is driven by both a leak flux and a secretory component.