Periodic Report Summary - GUT DCS IN IBD (Intestinal dendritic cells and gut T-cell homing in inflammatory bowel diseases)
Following conditioning with an intestinal microenvironment, human blood DC acquired a homeostatic 'gut-like' phenotype with all the associated phenotypic and functional characteristics of resident intestinal DC including a lower stimulatory capacity for T-cells as well as a gut-homing priming capacity on T-cells that they stimulated. On the contrary, if human blood enriched DC were conditioned with an IBD microenvironment they failed to acquire a homeostatic phenotype and became more stimulatory for T-cells. Interestingly, T-cells stimulated by IBD-conditioned DC failed to acquire a gut-homing restricted phenotype and on the contrary acquired an aberrant skin-homing profile providing a molecular explanation for the development of extra-intestinal manifestation (usually skin-associated) in some IBD patients.
We next aimed to identify which factors in healthy controls mediate the acquisition of a homeostatic gut-like phenotype by DC and which presumably are lost or masked in IBD patients. We have identified that both retinoic acid (RA) and TGFbeta have complementary roles in those processes. Intestinal RA controls the acquisition of a gut-homing profile both by DC and T-cells that they stimulate, although it did not have an effect on their stimulatory capacity. Intestinal TGFbeta on the contrary induced a lower stimulatory phenotype on conditioned DC although it did not participate in the mechanisms which control the gut-homing properties. Finally, if human blood enriched DC were pre-pulsed with RA prior to conditioning with an IBD microenvironment acquisition of a higher stimulatory phenotype as well as the capacity to generate aberrant skin-homing T-cells was abrogated; these finding provide new insights into the development of potential new tissue-specific therapies to prevent the inflammatory activities in the gut in IBD patients.
Finally, we have identified that the intestinal microbiota have a direct and essential role in controlling intestinal homeostasis through their capacity to modulate the phenotype of intestinal DC towards a regulatory or homeostatic phenotype. That unexpected finding is currently under study with some of our collaborators.
Our results have revealed that both TGFb and retinoic acid have a central role in humans controlling intestinal immune homeostasis. That evidence may help development of new tissue-specific therapies in IBD patients based in immuno-nutrition and / or development of DC vaccines.