An immunobiliary single-cell atlas resolves crosstalk of type 2 cDCs and γδT cells in cholangitis

Background and aims

The immunobiliary niche serves as a reservoir of tissue-resident immune cells, yet the role of unconventional T cells during cholangitis remains poorly understood. Here, we connect cell state dynamics of type 2 conventional dendritic cells (cDC2) in cholangitis with site-specific γδ T17 responses in liver and draining lymph nodes (LN).

Methods

The 0.1% Diethoxycarbonyl-1,4-Dihydrocollidine (DDC) diet was used to generate an immunobiliary DC- and γδ T-enriched mouse liver and LN single-cell RNA-sequencing (scRNA-seq) atlas covering temporal disease dynamics, resolution and cDC2B depletion. cDC2 trajectories were inferred using VarID2 and γδ T cell transcription factor (TF) regulon activity was predicted by SCENIC. The human biliary niche was resolved by integrating human liver scRNA-seq data with available spatial transcriptomics data. Functional studies were conducted using Tcrd knockout, Il17a/f knockout and Tcrd reporter mice.

Results

A disease trajectory of Mgl2 ⁺ cDC2B was identified connecting DC maturation, homing and the expression of Il17-inducing genes. Disease progression was associated with numeric exhaustion of mature cDC2B and recruitment of DC precursors. γδ T cells were the main Il17 producers and were subtyped into Il17a ^high Scart1 ⁺ V γ 6 ⁺ and Il17 ^low Scart2 ⁺ V γ 4 ⁺ populations exhibiting cDC2-directed communication and divergent TF regulon activity. Spatial proximity and conserved molecular interactions of cDC2 and γδ T cells were confirmed in human cholangitis. Il17-deficiency resulted in reduced liver fibrosis in mice, while cDC2B depletion attenuated γδ T17 cell states.

Conclusions

In cholangitis, a profibrogenic function of γδ T cells is contingent on the induction by peribiliary cDC2B, thereby highlighting relevant disease determinants within the immunobiliary and liver-draining LN niche.

Impact and Implications

The immunobiliary niche contains rare immune cells such as conventional dendritic cells and unconventional T cells, however, the function of these cell types in liver inflammation remains poorly understood. Mirroring human biliary diseases such as primary sclerosing cholangitis, we induced experimental cholangitis in a mouse model to generate a site-specific single-cell sequencing atlas resource resolving underexplored cell populations. Our data capture a profibrotic hepatic disease state trajectory of Mgl2 ⁺ cDC2B inducing a γδ T cell-specific Il17-response, which is attenuated upon cDC2B depletion and in DC precursors, which are characterized by reduced genomic accessibility of γδ T cell-interacting genes.

These results highlight the importance of portal niche residing underexplored immune cell populations and the necessity to further resolve immunobiliary niche responses and crosstalk in inflammatory settings such as in cholangitis.

Graphical Abstract