T cell specific deletion of Casitas B lineage lymphoma-b reduces atherosclerosis, but increases plaque T cell infiltration and systemic T cell activation

Introduction: Atherosclerosis is a lipid-driven inflammatory disease of the arterial wall, and the underlying cause of the majority of cardiovascular diseases. Recent advances in high-parametric immunophenotyping of immune cells indicate that T cells constitute the major leukocyte population in the atherosclerotic plaque. The E3 ubiquitin ligase Casitas B-lymphoma proto-oncogene-B (CBL-B) is a critical intracellular regulator that sets the threshold for T cell activation, making CBL-B a potential therapeutic target to modulate inflammation in atherosclerosis. We previously demonstrated that complete knock-out of CBL-B aggravated atherosclerosis in Apoe^-/- mice, which was attributed to increased macrophage recruitment and increased CD8⁺ T cell activation in the plaque. Methods: To further study the T cell specific role of CBL-B in atherosclerosis, Apoe^-/- CD4^creCblb^fl/fl (Cbl-b^cKO) mice and Apoe^-/-CD4^WTCblb^fl/fl littermates (Cbl-b^fl/fl) were fed a high cholesterol diet for ten weeks. Results: Cbl-b^cKO mice had smaller atherosclerotic lesions in the aortic arch and root compared to Cbl-b^fl/fl, and a substantial increase in CD3⁺ T cells in the plaque. Collagen content in the plaque was decreased, while other plaque characteristics including plaque necrotic core, macrophage content, and smooth muscle cell content, remained unchanged. Mice lacking T cell CBL-B had a 1.4-fold increase in CD8⁺ T cells and a 1.8-fold increase in regulatory T cells in the spleen. Splenic CD4⁺ and CD8⁺ T cells had increased expression of C-X-C Motif Chemokine Receptor 3 (CXCR3) and interferon-γ (IFN-γ), indicating a T helper 1 (Th1)-like/effector CD8⁺ T cell-like phenotype. Conclusion: In conclusion, Cbl-b^cKO mice have reduced atherosclerosis but show increased T cell accumulation in the plaque accompanied by systemic T cell activation.