Intestinal and hepatic dendritic cells in the induction of tolerogenic responses

  • Induktion tolerogener Immunantworten durch intestinale und hepatische Dendritische Zellen

Leufgen, Andrea; Pabst, Oliver (Thesis advisor); Clavel, Thomas (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022


Gut and liver build a functional entity, the so-called gut-liver axis, and act in concert to provide immunity and maintain tolerance to the gut microbiota as well as food derived antigens. Immune cells of the gut come into contact with luminal antigen through the epithelial layer, while the liver is exposed to oral antigen via portal vein blood. To perpetuate an overall tolerogenic status, two types of immune cells are of particular importance. Dendritic cells (DCs) are the main antigen presenting cells and therefore indispensable in both priming of protective immunity and maintaining immune tolerance to harmless antigen by inducing FoxP3+ regulatory T cells (Treg). In the steady state small intestine (SI), DCs induce unresponsiveness to orally delivered antigen, a mechanism referred to as oral tolerance. The liver also plays a role in tolerance induction and failure of oral tolerance can lead to inflammatory disorders such as food allergies or inflammatory bowel disease (IBD). In this thesis, we aimed to determine how DCs from gut and liver contribute to the induction of systemic tolerance. To address this, we examined if DCs of SI, colon and liver are able to pick up orally delivered antigen, migrate to draining lymph nodes (LNs) and activate T cells to become Treg. Furthermore we aimed to clarify how these Treg contribute to system-wide tolerance after oral antigen exposure by examining the homing patterns of newly activated T cells. We find that DCs from all three organs of the gut-liver axis are able to pick up oral antigen, subsequently migrate in lymph and present the antigen in draining LNs. While steady state DCs from SI, colon and liver showed overall phenotypic and transcriptomic similarity, they nevertheless exhibited several important differences, notably in directing the homing and differentiation of T cells. We found SI DCs to be most efficient in metabolising vitamin A derivatives which enhances their capacity to induce the retinoic acid (RA) dependent gut-homing factors CC type motif chemokine receptor (CCR) 9 and integrin alpha 4 beta 7 (Intα4β7) on newly activated T cells. Moreover, DCs migrating from the steady state SI, colon and liver were able to induce distinct T cell responses within the inductive compartment of the draining LNs. We established a photoconversion-based experimental model of in vivo T cell tracking and use it to demonstrate that oral administration of cognate antigen leads to T cell migration to distinct organs, dependent on the inductive LN compartment. Interestingly, our data shows that T cells primed in the SI-draining mesenteric LN (sMLN) subsequently migrate to SI, but also to colon and liver. In contrast, T cells activated in colon-draining MLN (cMLN) or liver-draining LNs (ldLNs) migrate exclusively to colon and liver, but not the SI. Notably, T cell homing correlated to a site-specific expression of chemotactic receptors. Thus, recently activated T cells that had migrated to the SI, colon and liver expressed high levels of CCR9, G protein coupled receptor (GPR) 15 and CXC-type motif chemokine receptor (CXCR) 3 respectively, suggesting a directed migration process to specific tissues orchestrated during T cell differentiation. Further studies will be necessary to characterise the molecular mechanisms that are responsible for the differential induction of chemokine receptor expression as well as delineate the relative contribution of the migrating DCs and the LN microenvironment in this process. However, in addition to directed homing, we found that a large proportion of T cells activated by oral antigen adopted a LN-resident phenotype. While their function or mechanisms of induction are unknown, one possibility is that these cells may be strategically positioned to prevent future adverse T cell priming and help maintain tolerance. In summary, our work contributes to a deeper understanding of the functionality of DCs and T cells within the gut-liver axis and extends the knowledge of how a tolerogenic environment is maintained, underlining the importance of a system-wide distribution of induced regulatory T cells after oral antigen exposure for future antigen encounters. Our data may aid in the development of new therapeutic strategies of for inflammatory disorders such as IBD or food allergies by characterising specific homing patterns of newly activated regulatory T cells after oral antigen exposure.