Background/Purpose: Autoimmune PolyEndocrinopathy Candidiasis Ectodermal Dystrophy (APECED) is a rare syndrome of multi-organ autoimmunity driven by the presence of self-reactive T cells and autoantibodies caused by mutations in the gene Autoimmune regulator (Aire). Compared to the well-defined role of Aire in establishing and maintaining T cell central tolerance by helping medullary thymic epithelial cells eliminate self-reactive T cells, less is known about how Aire deficiency in APECED impacts B cells and causes a breakdown in peripheral B cell tolerance. Methods: We performed single-cell sequencing analyses, flow cytometry, and autoantibody profiling of PBMCs and serum of 10 APECED patients and 10 controls. Results: We found robust changes in the B cell compartment of APECED patients relative to that of healthy donors, with a substantially lower percentage of naïve B cells and significant increases in antigen-experienced B cell phenotypes. Among these changes seen by scRNAseq compositional analysis were increases in Memory B cells (TACI+ CD27+), and Atypical B cells (CD21lo CD11c+ Tbet+). Serum autoantibody profiling with an array of ~23,000 proteins uncovered >200 APECED associated IgG autoantibody varieties, including to type I IFN, IL17, key enzymes including the cytochrome P450 family, neurotransmitter associated proteins, and others. The Atypical B cell subset in patients was found to be especially correlated to levels of IgG autoantibodies, and had a molecular signature enriched in antigen presentation and B cell activation genes. Conclusion: These results demonstrate that the B cell compartment is altered in APECED patients relative to healthy controls, with a marked increase in multiple activated B cell subsets that may contribute to autoantibody production and disease manifestations.
