Project Summary/Abstract Interleukin-38 (IL-38), a member of the IL-1 family, has not been studied until recently despite its discovery 20 years ago. It is a neglected cytokine because no receptor was identified for how IL-38 functioned. However, in 2012, we reported that recombinant human IL-38 bound to the IL-36 receptor (now IL-1R6) and suppressed the production of IL-17 and IL-22. In that study, we proposed that IL-38 acted as a receptor antagonist for IL-1R6. However, the dose-response of IL-38 did not behave as receptor antagonist but rather acted as an inhibitor of cell activities. New data suggests that IL-38 requires IL-1R6, an orphan receptor in the IL-1 Family, to suppress IL-17. Formerly termed IL-1 Receptor Associated Protein Like-1, IL-1R9 will be studied for its putative role in the suppression of innate immunity by recombinant IL-38. Using CRISPR/Cas methods, we have generated a colony of mice that are deficient in IL-38. These mice are used to determine a requirement for endogenous IL-38 in mouse models of human inflammatory diseases. In those models where disease severity worsens in IL-38 deficient mice, we will use recombinant IL-38 to treat mice for suppression of innate inflammation. In order to fully understand the role of IL-38 in innate immunity, we generated a mouse colony deficient in IL-1R9. We will study the requirement of IL-1R9 for the function of recombinant IL-38 in those mouse models where treatment with IL-38 has significantly reduced disease severity. A unique aspect of this application is that IL-1R9 in on the X-chromosome, an unusual finding in cytokine biology. Because IL-1R9 is on the X-chromosome, we can address how suppression of innate immunity is affected in males compared to females. With most autoimmune diseases having a 70% predilection for females and with each autoimmune disease there is an inflammatory contribution, we have designed studies for comparisons of homozygous IL-1R9 deficient males to homozygous IL-1R9 females. In these studies, we will also evaluate the role of IL-38 to inhibit the activation of the NLRP3 inflammasome using a specific oral NLRP3 inhibitor presently used to treat patients. In addition to AIM 1 and AIM 2 studies on recombinant IL-38 suppression of innate immunity and the putative role of IL-1R9, we will produce and test an IL-38-Fc fusion protein (AIM 3). The rationale for producing an IL-38-Fc fusion protein is to provide pre-clinical data for an IL-38 therapeutic. In AIM 4 we address the issue of IL-38 release from the cell. IL-38 circulates in healthy subjects but levels are significantly low in subjects at risk for a cardiovascular events. However, IL-38 being a B-cell product suggests that processing of the IL-38 precursor and release from the cell is not via traditional pathways. We will examine pathways for secretion that are used by other members of the IL-1 Family : inhibition of NLRP3 and inhibition of calpains. The overall goal of these studies is to advance th...