Abstract

Kawasaki Disease (KD), a pediatric acute febrile systemic vasculitis, is the leading cause of acquired heart diseases in children. Coronary artery aneurysms (CAAs) occur in up to 25% of untreated children, which is reduced to 5% with intravenous immunoglobulin (IVIG) treatment. However, up to 20% of KD patients are refractory to IVIG and at higher risk of developing CAAs. This highlights the need to characterize the immune mechanisms mediating KD to develop more efficient therapies. IL-1β plays a key role in KD pathogenesis. IL-33, a member of the IL-1 cytokine family, is released upon inflammation and tissue damage and exerts its effects by binding to its receptor ST2 ( Il1rl1 ). Circulating levels of IL-33 are elevated in KD patients during the acute phase of the disease. However, if and how IL-33 contributes to cardiovascular lesion development in KD remains unknown. Using the Lactobacillus casei cell wall extract (LCWE) murine model of KD vasculitis, we observed increased Il33 mRNA expression in hearts and abdominal aorta aneurysms of LCWE-injected mice. While ST2 was detected by immunofluorescence in the hearts of both control and LCWE-injected mice, its expression was increased in the abdominal aortas of LCWE-injected mice. In contrast, IL-33 expression was only increased in inflamed cardiovascular tissues of LCWE-injected mice. Single-cell RNA-sequencing and flow cytometric analysis of abdominal aortas, as well as spatial transcriptomics of heart tissues from LCWE-injected mice, indicated that Il33 transcripts were expressed primarily by stromal cells, such as fibroblasts, endothelial cells, and vascular smooth muscle cells. On the other hand, Il1rl1 transcripts were highly expressed by tissue infiltrating immune cells, such as macrophages, eosinophils, and neutrophils. Blocking IL-33, using either Il33 -/- mice or an anti-IL-33 antibody, significantly attenuated LCWE-induced KD vasculitis. In vitro, IL-33 treatment of LCWE-stimulated bone marrow-derived macrophages boosted their IL-1β production. Overall, our results indicate that IL-33, produced by stromal cells, may promote LCWE-induced KD vasculitis by increasing the release of IL-1β by tissue infiltrating immune cells, and this axis could therapeutically be targeted in KD.