Background: Previous studies have established that posthemorrhagic shock mesenteric lymph (PHSML) contains proinflammatory mediators, while the cellular basis of PHSML is less well characterized in acute models of injury. CD103 dendritic cells (DCs) have been identified in the mesenteric lymph (ML) in models of chronic intestinal inflammation, suggesting an important role in the gut response to injury. We have previously demonstrated the ability of vagal nerve stimulation (VNS) to prevent gut barrier failure after trauma/hemorrhagic shock (T/HS); however, the ability of VNS to alter ML DCs is unknown. We hypothesized that the CD103 MHC-II DC population would change in PHSML and that VNS would prevent injury-induced changes in this population in PHSML.
Methods: Male Sprague-Dawley rats were randomly assigned to trauma/sham shock or T/HS. T/HS was induced by midline laparotomy and 60 minutes of HS (blood pressure, 35 mm Hg), followed by fluid resuscitation. A separate cohort of animals underwent cervical VNS after the HS phase. Gut tissue was harvested at 2 hours after injury for histologic analysis. ML was collected during the pre-HS, HS, and post-HS phase. For flow cytometric analysis, ML cells were subjected to staining with CD103 and MHC-II antibodies, and this cell population was compared in the pre-HS and post-HS phase from the same animal. The CD4Foxp3 cell (T reg) population in the ML node (MLN) was also tested to determine effects of CD103 DC modulation in the ML.
Results: VNS reduced histologic gut injury and ML flow seen after injury. The CD103 MHC-II DC population in the PHSML was significantly decreased compared with pre-HS and was associated with decreased T reg expression in the MLN. VNS prevented the injury-induced decrease in the CD103 MHC-II+ DC population in the ML and restored the T reg population in the MLN.
Conclusion: These findings suggest that VNS mediates the inflammatory responses in ML DCs and MLN T reg cells by affecting the set point of T/HS responsiveness.