Background/Purpose: Blau syndrome, a pediatric rheumatological disease characterized by uveitis, arthritis, and dermatitis, is caused by a single point mutation in the gene NOD2. Nod2 is an intracellular pattern recognition receptor important for host defense against infection. Recent studies show Blau mutations result in a loss of function of NOD2 resulting in diminished bacterial sensing capacity, however, how mutated NOD2 results in sterile inflammation in Blau syndrome is unknown.  We recently showed that non-mutated Nod2 functions within T cells to inhibit Th17/IL-17-mediated experimental autoimmune uveitis and arthritis. Here we sought to investigate how Blau Nod2 mutations affect autoreactive Th17 responses and experimental autoimmune uveitis (EAU) pathogenesis.

Methods: Rag1^-/- mice were reconstituted with CD4 T cells isolated from naïve Nod2^R314Q or wildtype (WT) mice. After 7 days of reconstitution, peripheral blood CD4 T cell expression of transcription factor, Rorγt, was quantified by flow cytometry.  One day later, EAU was induced by immunization with the human retinal antigen, interphotoreceptor retinoid binding protein (IRBP_1-20), complete Freund’s adjuvant and pertussis toxin. Intraocular inflammation was assessed over time by genotype-masked clinical scoring of retinal images and histology from eyes collected on day 21 post immunization. Antigen-specific T cell responses were assessed by cytokine production via ELISA by restimulating splenocytes ex-vivo on day 21 post immunization with retinal peptide, IRBP. Data were analyzed by Mann Whitney U test, and p< 0.05 were considered significant.

Results: To study mechanisms of Blau syndrome pathogenesis our lab employs a unique knock-in mouse expressing the most common human Blau mutation, NOD2 R334Q (Nod2 R314Q). To understand how Nod2^R314Q T cells control CD4 T cell mediated autoimmunity in EAU, T cell-deficient Rag1^-/- mice were reconstituted with Nod2^R314Q or WT CD4 T cells and uveitis was induced 7 days later. WT and Nod2^R314Q T cell-recipient mice had equal T cell reconstitution as measured by CD4+ T cells in circulation at 7 days, however, Nod2^R314Q T cell recipients had increased expression of the Th17-associated transcription factor, Rorγt, (15% of CD4+) compared to WT T cells (7.5% of CD4+), indicating Nod2^R314Q enhances Th17 responses during non-infectious T cell homeostasis. Twenty-one days post immunization Nod2^R314Q T cell recipients had more severe uveitis including increased retina (IRBP)-specific IL-17 production compared to WT T cell recipients. These data indicate that T cells expressing the Nod2^R314Q mutation are sufficient to cause exacerbated Th17-mediated uveitis.

Conclusion: Our data suggest Nod2^R314Q enhances Th17 immunity, and the pathogenesis of T cell mediated uveitis. This study reveals the potential role of T cells and IL-17 in Blau syndrome pathogenesis and highlights the need to investigate T cell-based therapies for Blau syndrome and other NOD2-mediated diseases.  

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/mutated-nod2-enhances-pathogenic-th17-responses-that-promote-experimental-blau-syndrome/