Background/Purpose: Mutations in nucleotide-binding oligomerization domain-containing protein 2 (NOD2) cause Blau syndrome, an inflammatory disorder characterized by uveitis, dermatitis, and polyarthritis. The antimicrobial functions of NOD2 are well established; yet the mechanism by which dysregulated NOD2 causes sterile inflammation remain unknown. Here we utilized experimental models of autoimmune arthritis and uveitis, and PBMCs from Blau syndrome patients to dissect a T cell-specific role for NOD2 in uveitis.

Methods: Arthritis was induced in SKG and NOD2^-/-SKG mice with a single intraperitoneal 1.5mg injection of zymosan and assessed by clinical scoring, near infrared imaging and histology. Uveitis was induced in NOD2^+/+ and NOD2^-/- C57BL/6 mice by immunization with the retinal antigen interphotoreceptor retinoid-binding protein (IRBP) and assessed by clinical scoring and histology. Mice were treated with IL-17A/F mAb (R&D systems) beginning 24h prior to disease induction. Lymphopenic Rag1^-/- mice were reconstituted with NOD2^-/- or NOD2^+/+ (WT) CD4+ T cells and arthritis or uveitis was induced. IL-17 production by T cells was evaluated by flow cytometry and ELISA. For T cell homeostasis studies, purified naive (CD62L^hiCD44^–) CD4+ T cells were differentiated under Th17 polarizing conditions (CellXVivo) or purified memory (CD62L^–CD44^hi) CD4+ T cells from naive mice were stimulated with anti-CD3 and anti-CD28, and activation state (CD69) and pro-inflammatory cytokine production was determined by flow cytometry (n≥6 mice/group and repeated 3X). Peripheral blood mononuclear cells from Blau Syndrome patients or healthy controls were cultured for 5 d, stimulated with PMA/ionomycin, and IL-17 was measured. Data were analyzed by Mann-Whitney, and p< 0.05 were considered significant.

Results: Lymphopenic recipients of NOD2-deficient T cells developed significantly worse arthritis and uveitis, implicating T cell-intrinsic NOD2 in suppression of disease. CD4+ T cells purified from arthritic and uveitic mice produced significantly more IL-17, and blockade of IL-17 mitigated the enhanced disease caused by NOD2-deficiency, indicating a direct role for T cell-intrinsic NOD2 in suppressing autoreactive Th17 responses. NOD2 was dispensable for Th17 differentiation of naïve CD4+ T cells. However, NOD2^-/- memory (antigen-experienced) CD4+ T cells isolated from naïve mice when stimulated with anti-CD3 and anti-CD28 had enhanced expression of IL-17, the IL-17-associated transcription factor (RORγt) and the activation marker CD69. Importantly, stimulation of CD4+ T cells from Blau syndrome patients resulted in significantly more IL-17 production than those from healthy control T cells, suggesting a similar function for NOD2 in human disease.

Conclusion: We have uncovered a novel, T cell-intrinsic function for NOD2 as a negative regulator of T cell homeostasis and autoimmunity. Our work suggests that a “loss-of-function” in NOD2 (i.e. NOD2^-/- mice) results in a “gain-of-function” in the ability of T cells to produce IL-17 and cause arthritis and uveitis. These findings could potentially change the way we view the immunopathology of Blau syndrome and open up new therapeutic options for patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-t-cell-intrinsic-role-for-nod2-in-suppression-of-th17-mediated-experimental-arthritis-and-uveitis-implications-for-blau-syndrome/