Retinoic Acid Receptor-Related Orphan Nuclear Receptor γt Licenses the Differentiation and Function of a Unique Subset of Follicular Helper T Cells in Response to Immunogenic Self-DNA in Systemic Lupus Erythematosus

Objective Accumulating studies have identified self-DNA as driving IgG anti-double-stranded DNA (anti-dsDNA) in lupus, though the underpinning mechanisms of this process remain largely undefined. Here, we explored the activity of transcription factor retinoic acid receptor-related orphan nuclear receptor gamma t (ROR gamma t) in the differentiation and function of self-DNA-specific follicular helper T (Tfh) cells in lupus. Methods B6, TCR alpha(-/-), CD4(-/-), ROR gamma t(fl/fl)CD4Cre, ROR gamma t(+/+)CD4Cre, Bcl-6(fl/fl)CD4Cre, Bcl-6(+/+)CD4Cre, IL-17(-/-), and ICOS-/- mice were immunized with normal self-DNA, immunogenic self-DNA, and pathogen DNA to induce the production of Tfh cells and IgG anti-dsDNA. Tfh cells with or without interleukin-17 (IL-17) were evaluated for their role in supporting the generation of IgG. NSG mice were reconstituted with immune cells and circulating DNA from human subjects for translational studies. IL-17-positive Tfh cells were analyzed for their correlation with IgG anti-dsDNA levels as well as their response to circulating self-DNA in lupus patients. Results Unlike normal self-DNA, immunogenic self-DNA and pathogen DNA efficiently induced IgG responses. Immunogenic self-DNA induced IgG in a CD4+ T cell-dependent manner, which was abrogated by ROR gamma t deficiency. In contrast, ROR gamma t was not required for the generation of pathogen DNA-induced IgG. Further analyses identified ROR gamma t as essential for the differentiation and function of Tfh cells in response to immunogenic self-DNA, assigning IL-17 as a feature cytokine. These IL-17-positive Tfh cells functioned independent of inducible costimulator (ICOS), critically supporting IgG generation. Targeting immunogenic self-DNA-specific Tfh cells by ROR gamma knockdown and IL-17 blockade ameliorated IgG response and lupus nephritis in a humanized mouse model. The presence of IL-17-positive Tfh cells was associated with IgG anti-dsDNA levels and were expanded by circulating immunogenic self-DNA in lupus patients. Conclusion Immunogenic self-DNA instructs ICOS-dispensable IL-17-positive Tfh cells via ROR gamma t to produce an IgG anti-dsDNA response. As such, IL-17-positive Tfh cells are a promising therapeutic target for lupus patients.

Automated summary

Accumulating studies have identified self-DNA as driving IgG anti-double-stranded DNA (anti-dsDNA) in lupus, with the transcription factor ROR gamma t playing a key role in the differentiation and function of self-DNA-specific follicular helper T (Tfh) cells.