The autoimmune disease systemic lupus erythematosus (SLE) is a complex disease caused by dysregulated immune cell activation and function. Generally, immune cells in the body only become activated when they are exposed to a pathogen, such as a virus or bacteria. However, in SLE patients, their immune cells are always reacting to an invading foreign pathogen(s), yet the pathogen(s) is not foreign, it is from self. This constant assault on the immune system by self results in the generation of antibodies against self that ultimately cause the destruction of tissues and organs seen in SLE patients. How this assault on the immune system begins is still not clear but it is known that SLE can be inherited, supporting the idea that inherited genetic variants may contribute to SLE disease onset and severity.

Genetic variants in the transcription factor interferon regulatory factor 5 (IRF5) have been robustly associated with SLE susceptibility (risk) in multiple groups of people with different ancestral backgrounds. IRF5 is an important regulator of the immune system and others and we have shown that IRF5 expression and activation are significantly elevated in immune cells from SLE patients. What is not known is whether increased IRF5 expression and activation are due to risk variants or other disease-associated factors. To begin to address this, we examined IRF5 genotype-phenotype effects in healthy donors that carry the IRF5 homozygous risk or non-risk haplotype. Surprisingly, we did not detect differences in IRF5 expression between leukocyte subsets from risk and non-risk donors. Instead, we detected IRF5 hyper-activation in plasmacytoid dendritic cells (PDC), elevated numbers of circulating plasmablasts, spontaneous NETosis, and positive anti-nuclear antibody (ANA) staining in risk donors. Many of these phenotypes are detected in SLE patients and associate with disease severity.

To begin to test whether IRF5 hyper-activation may be a driver of SLE disease risk, onset, and severity, we determined the kinetics of Irf5 expression and activation in the NZB/W F1 model of spontaneous murine lupus. Somewhat surprisingly, we detected a distinct peak of elevated Irf5 activation that correlated with early disease onset. We injected NZB/W F1 mice for a two-week period (from 8 to 10 weeks of age) with a novel IRF5 inhibitor that directly binds to and inhibits IRF5 activation. In the treatment group, we found a significant reduction in proteinuria, serum dsDNA levels, and ANA staining that correlated with a significant increase in survival as compared to mock-treated mice. Based on these preliminary findings, we hypothesize that IRF5 hyper-activation is a driver of SLE disease onset and severity and that targeting the inhibition of IRF5 activation will protect mice and humans from the mortality associated with SLE. This hypothesis will be stringently tested in human healthy immune cells, SLE immune cells, and NZB/W F1 mice using a combination of biochemical, molecular, and cellular techniques.

Upon completion of this project, multiple components of the FY17 LRP Focus Areas will be addressed that are relevant to SLE patients: What is the contribution of IRF5 genetic risk to disease susceptibility? How does IRF5 contribute to SLE pathogenesis? Is IRF5 hyper-activation related to disease onset and/or later stages of relapse, flare, and kidney disease? What would be the outcome from treating an SLE patient with an IRF5 inhibitor? Will it cause global immunosuppression or a targeted effect? And, last, will an IRF5 inhibitor be therapeutically efficacious only in certain groups of SLE patients and/or at certain stages of the disease?

Results from this study will provide critical new functional and mechanistic insight into SLE genetic risk and the molecular drivers of SLE disease onset and mortality. It is expected that outcomes from this research will provide the critical rationale and scientific support for targeting IRF5 hyper-activation in the near future to prevent and treat SLE.