Revisiting the critical role of Th17 cell plasticity in the Peyer’s patch for gut IgA responses using single cell analysis unexpectedly demonstrated unperturbed responses to oral immunization in their complete absence

Gut Th17 cells are present at the Peyer’s patch inductive site as well as at the lamina propria effector site of the intestinal immune system. These cells are responsive to pathogens as well as to the commensal microbiota and they appear to be critical for gut homeostasis. While they have been associated with immune protection against pathogens they are also known to drive autoimmune inflammation in the gut. Hence, plasticity is a hallmark of gut Th17 cells and pro- as well as anti-inflammatory functions can be expected. This places Th17 cells at center stage for immune regulation of the gut immune system. However, their role for gut IgA responses to oral immunization awaits to be better defined, although earlier studies suggested that Th17 cells play a central role as their plasticity can convert them into follicular helper T (Tfh) cells that stimulate IgA class-switching and drive gut IgA responses. Here we used an IL-17 fate-reporter mouse and a cholera toxin B-subunit (CTB)-specific tetramer to isolate CTB-specific CD4 T cell subsets following oral immunization with CT. We found no evidence of CTB-specific Th17 development in the PP, rather a clear dominance of Tfh cells was observed. Single-cell RNAseq analysis revealed a massive clonotypic dominance of Tfh cells, but no Th17 or regulatory T cells (Tregs) were found among the CTB-tetramer-specific CD4 T cells. While 3 clusters of Tfh cells were found only one cluster hosted the CTB-specific CD4 T cells. An adoptive transfer of rorgt-deficient CD4 T cells into nu/nu recipient mice exhibited unperturbed gut IgA responses to oral CT immunization, clearly demonstrating that Th17 cells are, indeed, dispensible for gut IgA responses following oral immunization.