HSV-1 infection of enteric nervous system evokes inflammation-mediated myenteric plexus injury.

Objective: Enteric neuropathies are characterized by marked infiltration of neutrophils and cytotoxic lymphocytes into the myenteric plexus. We previously reported that Herpes simplex virus (HSV)-1 infection of the enteric nervous system (ENS) results in neuro-dysfunction and gastrointestinal dysmotility. Since the mechanisms of neuronal injury remain unclear, in the present study we investigated whether innate and/or acquired immune responses against HSV-1 harm neuronal functional integrity. Methods: Adult C57Bl/6 mice were intranasally inoculated with HSV-1, after 4 weeks (W) intragastrically (IG), and sacrificed 1–8 W post IG. Molecular analysis was performed to ascertain viral transcripts in longitudinal muscle myenteric plexus (LMMP). Immune cells isolated from mucosa and LMMP were characterized using fluorescent activated flow cytometry (FACS). Muscular contractility and gut motility were evaluated by electric field stimulation (EFS) of isolated ileal segments and gastrointestinal transit, respectively. ENS integrity was assessed by immunofluorescence on LMMP whole mount preparations for peripherin expression. Results: In the ENS of infected mice, HSV-1 latencyassociated transcripts (LATs) correlated with the infiltration of activated macrophages (CD11b+CD49d+F4/80+ cells) and CD4+CD25+Foxp3+ regulatory T cells at 2 and 6 W post IG viral inoculum. Abortive viral replication was associated to HSV-1 reactive CD3+CD8+IFNgamma+ lymphocytes at 8 W post IG. EFS-evoked contractions were reduced at 2 W post infection but increased at 8 W. Intestinal transit time was reduced only at 8 W post IG infection as compared to sham infected animals. In myenteric plexus, peripherin expression augmented during the early time of infection but resulted highly fragmented at 8 W. Administration of anti-serum anti-CD8 at 6 W post IG infection ameliorated intestinal contractility in mice sacrificed at 8 W. Conclusion: In the ENS, HSV-1 infection triggers innate and acquired immune responses in a timedependent fashion. Thus, following neurotropic viral infection the recruitment of different immune-competent cellular populations into the myenteric plexus may account for the time-dependent neuronal damage and intestinal dismotility during enteric neuropathies.