The immune mechanisms underlying Kawasaki disease (KD), a febrile systemic vasculitis in children, are poorly understood. Reports indicate elevated levels of circulating IL-33 in acute KD patients; however, if IL-33 contributes to the pathogenesis of KD vasculitis remains unclear. Here, we used the Lactobacillus casei cell wall extract (LCWE)-induced murine model of KD to determine the contribution of IL-33 to vasculitis development. We observed increased expression of Il33 transcripts and IL-33 protein in LCWE-induced cardiovascular lesions. Bone marrow chimera experiments suggest that IL-33 production by both hematopoietic and stromal cells is important for LCWE-induced KD vasculitis; however, single-cell RNA sequencing, spatial transcriptomics, and flow cytometric analysis revealed that stromal cells were the predominant sources of IL-33. Furthermore, immune cells infiltrating LCWE-induced cardiovascular lesions expressed Il1rl1 transcripts, coding for the IL-33 receptor ST2. In vitro stimulation of bone marrow-derived macrophages with IL-33 enhanced their production of IL-1b and TNF-α. In vivo blockade of IL-33, using either neutralizing IL-33 antibody or Il33-/- mice, effectively attenuated LCWE-induced cardiovascular inflammation. Our results indicate that IL-33 contributes to LCWE-induced vascular inflammation through redundant mechanisms across multiple immune cell subsets rather than a single population and highlight IL-33 as a potential therapeutic target. © The Author(s) 2025. Published by Oxford University Press on behalf of British Society of Immunology. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.