The CCR6/CCL20 axis expands RORγt+ Tregs to protect from glomerulonephritis

Abstract

Previous studies have identified a unique Treg population, which expresses the Th17 characteristic transcription factor RORγt. These RORγt⁺ Tregs possess enhanced immunosuppressive capacity, which endows them with great therapeutic potential. However, as a caveat, they are also capable of secreting pro-inflammatory IL-17A. Since the sum function of RORγt⁺ Tregs in glomerulonephritis (GN) remains unknown, we studied the effects of their absence. Purified CD4⁺ T cell populations, containing or lacking RORγt⁺ Tregs, were transferred into immunocompromised RAG1 knockout mice and the nephrotoxic nephritis model of GN was induced. Absence of RORγt⁺ Tregs significantly aggravated kidney injury, demonstrating overall kidney-protective properties. Analyses of immune responses showed that RORγt⁺ Tregs were broadly immunosuppressive with no preference for a particular type of T cell response. Further characterization revealed a distinct functional and transcriptional profile, including enhanced production of IL-10. Expression of the chemokine receptor CCR6 marked a particularly potent subset, whose absence significantly worsened GN. As an underlying mechanism, we found that chemokine CCL20 acting through receptor CCR6 signaling mediated expansion and activation of RORγt⁺ Tregs. Finally, we also detected an increase of CCR6⁺ Tregs in kidney biopsies, as well as enhanced secretion of chemokine CCL20 in 21 patients with anti-neutrophil cytoplasmic antibody associated GN compared to that of 31 healthy living donors, indicating clinical relevance. Thus, our data characterize RORγt⁺ Tregs as anti-inflammatory mediators of GN and identify them as promising target for Treg directed therapies.

Keywords: Treg-directed therapy; chemokine; chemokine receptor; crescentic GN; immunosuppression.