DOP019IL-18 as an enhancer of the pathogenic memory Th1/Th17 phenotype in pediatric Inflammatory Bowel Disease

Abstract Background In Crohn’s disease (CD) and ulcerative colitis (UC), memory T helper (Thm)17 cells can become plastic and acquire a pathogenic Thm1-like phenotype with IFN-γ production, denoted as ex-Thm17. We detected elevated plasma IL-18 concentrations in therapy-naïve pediatric CD and UC patients, decreasing with therapy. IL-18 enhances IL-12-induced IFN-γ production by Th1 cells, yet its role in Th17 plasticity in CD and UC is unclear. We hypothesized that IL-18 plays a pathogenic role in CD and UC by stimulating Thm17. Methods From the PIBD-SETQuality cohort, therapy-naïve pediatric CD and UC patient plasma proteomics (92 proteins; CD: n = 85; UC: n = 31; control: n = 25), circulating gut-homing Thm populations, intestinal biopsy transcriptomes (CD: n = 57, UC: n = 21, control: n = 12) and immunohistochemistry (CD: n = 40; UC: n = 20), IBD-related SNP genotypes, and clinical parameters were examined. IL-18 receptor (IL-18R) expression and cytokine responses of in vitro stimulated healthy-donor Thm were determined by flow cytometry. Results Plasma IL-18 concentrations correlated to Th1-like plasma proteins in both CD (IFN-γ, CXCL9, CXCL11, CXCL10, PDL1, CDCP1) and UC (IFN-γ, CXCL9, CDCP1). In UC, IL-18 concentrations also correlated to Th17-like plasma proteins (IL-17A, IL-12B, IL-17C), suggesting IL-18 may modulate both ex-Thm17 and Thm17 responses. In CD, IL-18 concentrations correlated to worse clinical disease activity scores and frequencies of circulating gut-homing ex-Thm17 (CCR6+CCR4+CXCR3+) cells, a population associated with a more severe disease course in CD. Interestingly, CD patients carrying the IL18R SNP rs6708413 had reduced Th1-like plasma protein concentrations and lower gut-homing ex-Thm17 frequencies, together arguing for a relationship between IL-18, ex-Thm17, and disease severity. In the intestine, increased mRNA expression of IL-18 pathway genes, and IL-18R, associated with more severe histological inflammation in CD and UC. Intestinal IL18R mRNA expression correlated to the number of infiltrating calprotectin+ cells in CD, whereas in UC, it correlated to infiltration of IL-17+ Thm. To study the role of IL-18 in ex-Thm17 and Thm17 programming, we restimulated Thm cells in vitro. Reactivation, particularly with IL-12, increased IL-18R expression on gut-homing Thm, indicating high potential to respond to IL-18 in an inflammatory setting. Moreover, IL-18 + IL-12 stimulation increased IL-17A+ and IFN-γ+ Thm17-like cell frequencies, favoring a synergistic role of both cytokines in ex-Thm17 and Thm17 modulation. Conclusion We identify IL-18 as a modulator of Thm17 responses, promoting a shift towards the IFN-g pathway while enhancing IL-17A production, thereby contributing to disease severity in patient subgroups. Conflict of interest: Grillmaier, Meike: No conflict of interest Barendregt, Danielle: No conflict of interest Calado, Beatriz: No conflict of interest Heredia, Maud: No conflict of interest Smits, Wilco: No conflict of interest Tuk, Bastiaan: No conflict of interest Hulleman-van Haaften, Danielle: No conflict of interest van Berkel, Lisette: No conflict of interest Klomberg, Renz: No conflict of interest Vuijk, Stephanie: No conflict of interest Doukas, Michail: No conflict of interest de Ridder, Lissy: No conflict of interest Escher, Johanna Caroline Hankje: No conflict of interest Samsom, Janneke N.: No conflict of interest