Neutrophil extracellular traps deficiency aggravates Citrobacter rodentium infection and the associated intestinal inflammation

Abstract

Abstract Peptidyl arginine deiminase-4 (PAD4) is required for the formation of neutrophil extracellular traps (NETs), which is part of the host antimicrobial innate immune response. However, the role of NETs in the pathogenesis and clearance of Citrobacter rodentium (a well-characterized mouse enteropathogen) infection remains unclear. In this study, we challenged the PAD4-deficient (Pad4KO; NETs-deficient) and WT littermates with C. rodentium. Luminal colonization of C. rodentium in Pad4KO mice peaked between 11-14 days post-infection (pi), whereas WT mice cleared the infection with no detectable level of the pathogen in fecal shedding after 7-10 days. Bacterial dissemination to spleen and mesenteric lymph node was significantly higher in Pad4KO mice at day 8 and 28 pi compared to WT. Additionally; Pad4KO mice displayed splenomegaly, colomegaly and elevated colonic and systemic pro-inflammatory markers (lipocalin 2 and serum amyloid A). Histological analysis demonstrated that transmissible colonic hyperplasia and goblet cell depletion were more pronounced in Pad4KO mice. Pad4KO mice also exhibited epithelial barrier dysfunction as indicated by their heightened serum immunoreactivity to bacterial proteins. Flow cytometric analysis revealed a substantial reduction in IL-10-producing macrophages and Th17 cells in the lamina propria and spleens of Pad4KO mice compared to WT mice. However, colonic expression of IL-17A and IL-22 were highly elevated in Pad4KO mice on day 8 pi, but were attenuated on day 28 both in Pad4KO and WT mice. Taken together, our findings highlight that NETs are indispensable in promoting clearance of C. rodentium and resolving the associated intestinal inflammation.