The greater splanchnic nerve preferentially regulates neutrophils over macrophages in a rat model of septic peritonitis

The sympathetic splanchnic nerve is a major player in immunoregulation, but its specific roles during infection have yet to be elucidated. Here, we evaluated how bilateral ablation of the greater splanchnic nerve (SplancX) impacts bacterial burden and immune function in a rat model of E. coli-induced septic peritonitis. SplancX had a major effect on bacterial burden within 24 h, reducing it to 4 % in the peritoneum and to 8 % in the spleen of what was found in the sham-operated controls. Such a major effect was not explained by gross changes in the infiltration of these sites with innate immune cells (neutrophils and macrophages), as assessed by flow cytometry. Single-cell RNA sequencing was then employed to evaluate the cellular activation programs of leukocyte subsets. Of the nine cellular clusters identified in the peritoneum of the infected rats, three of them had a transcriptional signature of activated neutrophils and two of them corresponded to quiescent neutrophils with an immunosuppressive signature. SplancX shifted the balance between these neutrophil subsets in a way consistent with heightened immunity, i.e., the activated neutrophils were augmented whereas the quiescent neutrophils were reduced in the SplancX group. The remainder of the clusters consisted of macrophages and erythrocytes, none of which changed in a way that could account for the observed effects on bacterial clearance. Confirming that SplancX resulted in heightened neutrophil activation, protein markers of neutrophil degranulation and NETosis were found to be elevated in the peritoneal lavage of the SplancX group. Taken together, the data show that the splanchnic nerve exerts a major effect on bacterial clearance in the acute phase of infection, presumably owing to selective changes in the balance between microbicidal and quiescent subsets of neutrophils.