Spatial multi-omics implicates vascular adipocytes proximal to tertiary lymphoid structures in human aortic aneurysm and B-cell autoreactivity.

Objective: Perivascular Adipose Tissue (PVAT), tertiary lymphoid structures (TLS), and the B lymphocytes they harbor have been implicated in regulating vascular diseases, including abdominal aortic aneurysm (AAA). Yet, the relationship of adipose tissue to TLS and B-cell responses is poorly understood. Approach and Results: Here, using multi-omics approaches, we characterized the potential interplay of vascular adipocytes and TLSs in shaping microenvironments conducive to pathogenic B-cell immunity in human AAA pathology. Single-nucleus RNA sequencing identified white adipocytes expressing transcripts for lipogenesis, lipolysis, and extracellular remodeling. Unexpectedly, these adipocytes expressed haptotactic and chemotactic factors such as thrombospondin 1 and autotaxin, and extracellular matrix proteins with potential to recruit CD44+ leukocytes within AAAs. Immunohistology revealed two anatomical compartments for the adipocytes within AAAs: PVAT and the medial-adventitial region. Medial-adventitial adipocytes were frequently associated with CD44+ TLSs and were largely absent from control non-aneurysmal abdominal aortas. Visium HD spatial transcriptomics revealed mature TLSs recapitulated the organization of functional secondary lymphoid structures, with multiple B-cell follicles clustered to form a nodular structure partly covered by a layer of smooth muscle cells. The TLSs harbored isotype-switched B cells expressing IgG1, IgG3, or IgA, with dominant kappa chain usage and IgG antibodies to the aortic wall. Myeloid cells in AAA were implicated in promoting B-cell effects, as they were the primary producers of B-cell activating factor (BAFF), a cytokine that promotes B-cell infiltration, survival, and function. Conclusion: Altogether, our results support a model in which new adipocytes in the medial-adventitial layer elicit inflammatory pathways that promote early TLS formation, and BAFF produced by myeloid cells promotes the survival and maturation of vascular wall-antigen-exposed B cells, leading to mature TLS formation, production of antibodies to AAA antigens, fueling inflammation and AAA growth.