The role of GGT5+ fibroblasts in leukocyte compartmentalisation in the gut and synovium

Thesis

The spatial organisation of leukocytes within tissues is essential for coordinated immune responses. While stromal cells such as fibroblasts are well known to structure leukocyte niches in secondary lymphoid organs (SLOs), their role in organising immune cells within inflamed non‑lymphoid tissues remains unclear. Building on mechanisms described in germinal centres (GCs), where follicular dendritic cells (FDCs) restrict B cell movement through the GGT5–GGG–P2RY8 axis, this thesis tests the hypothesis that stromal programs, particularly the induction of GGT5 by fibroblasts, establish perivascular confinement zones that spatially position P2RY8⁺ leukocytes within inflamed synovial and intestinal tissues.

Analysis of publicly available single-cell RNA-sequencing datasets revealed that GGT5, an enzyme shaping local gradients of the inhibitory ligand GGG, is broadly expressed by stromal cells across multiple inflamed tissues. In most tissues, GGT5 expression is restricted to endothelial cells and pericytes, but in RA synovium it expands beyond vascular rings into neighbouring fibroblasts, whereas in gut it is broadly distributed, forming a perivascular gradient associated with vascular activation. TNFα and NOTCH3 ligands induce GGT5 in synovial fibroblasts, while endothelial‑cell–derived factors stimulate GGT5 in both synovial and intestinal fibroblasts, suggesting that vascular–stromal communication provides an endothelium‑linked cue during inflammation.

Functionally, GGG inhibited CXCL12‑ and CXCL13‑directed migration of human tonsil T follicular helper (Tfh) and GC B cells, and Tfh from inflamed gut, consistent with P2RY8‑dependent immobilisation. Pilot live‑imaging provides an analysis framework for quantifying chemotactic index and speed under GGG. As inflammation unfolds, leukocytes infiltrate via blood vessels, triggering neighbouring fibroblasts to upregulate GGT5 expression. This facilitates the establishment of a perivascular confinement zone, wherein GGT5⁺ fibroblasts, through the GGT5–GGG–P2RY8 axis, regulate the motility and positioning of P2RY8⁺ leukocytes, contributing to leukocyte compartmentalisation.

Complementary murine colitis and arthritis models probe Ggt5 biology in vivo. However, mice lack P2RY8, limiting direct inference about GGG–P2RY8 signalling. Given that Ggt5 also participates in the leukotriene pathway, in vivo experiments have explored alternative roles for Ggt5 beyond P2RY8 signalling. Together, the data in this thesis supports a model in which endothelial activation and fibroblast GGT5 induction establish perivascular confinement zones that tune leukocyte positioning in IMIDs. These findings motivate the development of tools to map GGG in situ and suggest therapeutic strategies to modulate GGT5 activity to either stabilise protective niches or disperse pathogenic aggregates in RA and IBD.

Authors: Wong, Z

• DOI: 10.5287/ora-rdkjrdprd
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: fibroblast; inflammation; GGT5; migration
• Subjects: Leukocyte migration