New research shows disease-causing mutation doesn’t incite inflammation — it fails to prevent inflammation.

Arthritis, papular skin rashes and uveitis characterize the pediatric disease Blau syndrome. Before they reach kindergarten, children with this degenerative inflammatory condition experience impaired mobility, irreversible eye damage and vision loss. Blau is caused by a mutation in the gene NOD2, which is also associated with other inflammatory diseases, including Crohn’s disease. Exactly how the NOD2 variant causes Blau syndrome remains unknown.

New understanding may bring new treatment opportunities

Photo above, left to right: Ruth Napier with co-authors and lab members Holly Rosenzweig, Ph.D., Ellen Lee, Ph.D., Emily Vance, and Sydney Lashley with lab members Kofi Asare-Konadu, Nikita Farhaj, and Kylie Koney.

NOD2 was identified around 20 years ago, where it was shown to sense bacteria and other pathogens in innate immune system cells, like macrophages and neutrophils, and initiate an antimicrobial response via a defined pathway. A decade ago, a high-profile research paper reported that NOD2 functions within T cells; however, research from a second group refuted this, and the conclusion that NOD2 did not involve T cells has since been widely accepted.

In a paper published in Nature Communications, OHSU researchers show that NOD2 does, in fact, function within T cells — and through a totally novel pathway. NOD2 suppresses pathogenic T cells that cause arthritis and uveitis in Blau syndrome.

We’ve been so focused on thinking of NOD2 in a very particular way that we may have missed opportunities for T cell-based therapies that are well-tolerated and readily available.”

“Our findings have major implications in the field of autoimmunity, and could be really exciting for treating Blau syndrome,” said lead author Ruth Napier, Ph.D., a principal investigator with VA Portland Health Care System and an assistant professor in the OHSU Department of Molecular Microbiology and Immunology. “As scientists, we’ve been so focused on thinking of NOD2 in a very particular way that we may have missed opportunities for T cell-based therapies that are well-tolerated and readily available.”

Researchers have been focused on NOD2 in the context of its known role within innate cells in preventing infection, not in the context of T cell-mediated inflammatory diseases like uveitis and arthritis. Napier demonstrates that, in these contexts, NOD2 mutations specific to those found in Blau Syndrome patients fail to prevent inflammation rather than activating proinflammatory functions. This new understanding of the immunopathogenesis of Blau syndrome provides may change the way this disease is treated.

A new direction

“This paper is so monumental in this field — it really clarifies how, in the context of diseases like uveitis and arthritis, NOD2 is functioning in the T cell via a totally novel pathway,” said co-author Holly Rosenzweig, Ph.D., associate professor of molecular microbiology and immunology. “In patient samples, the team isolated T cells from Blau patients and did similar studies as with the mice, and replicated the same mechanism.”

To demonstrate the mechanism by which NOD2 functions and where the phenotype fit, Napier and her team bred three new mouse lines. Her lab is one of the few in the world with mice bred specifically to study Blau syndrome.

The lab performed T cell transfers, where they removed T cells from NOD2-deficient mice and put them in wild-type recipients so that T cells were the only cell type lacking NOD2. These experiments demonstrated that NOD2 is controlling T cells directly, by suppressing markers associated with autoreactivity.

“We induced uveitis in mice that lacked NOD2 only in T cells,” said Napier. “We were able to pin the cause on the T cells and NOD2, because every other cell had functioning (wild type) NOD2 and the disease was still very acute.”

These findings support in uveitis what  Napier and the Rosenzweig lab reported in their 2018 Journal of Immunology paper “NOD2 deficiency augments Th17 responses and exacerbates autoimmune arthritis”; NOD2 can act as a suppressor of arthritis and of uveitis.

A passion for translation: Lab to clinic

One of the main goals of the Napier lab is to understand how NOD2 drives inflammation in Blau in humans, with the end goal of developing new therapies for children with this rare disease.

Napier faces challenges present in all rare disease research: small sample sizes and reaching patients with the disease. About 4,000 children in total may have Blau syndrome in the U.S. In the course of her research, Napier connected with the Cure Blau Syndrome Foundation. That relationship is helping her address these challenges, as well as providing inspiration.

Napier and her research on Blau syndrome were featured in the film RARE HUMANS: Turning Hope into Action. The film features eight families advocating for research into rare diseases, 80 percent of which are genetic in nature.

Because NOD2 plays an important role across the immune system, Napier’s research will have implications not only for Blau syndrome but for other immunoinflammatory diseases as well.

This work was supported by funding from the National Institutes of Health (EY025250, EY025039 to H.L.R.), Department of Veterans Affairs, Biomedical Laboratory Research & Development Service (Merit award I01 BX002180 to H.L.R. and Career Development Award 1 IK2 BX004523 to R.J.N.), Medical Research Foundation of Oregon (R.J.N.), the Gerlinger Foundation (H.L.R.), Portland VA Research Foundation (PVARF), National Eye Institute intramural support (EY00184), and Australian Research Council (FT130101648).