The common variable immunodeficiency IgM repertoire narrowly recognizes erythrocyte and platelet glycans

Background Autoantibody-mediated cytopenias (AICs) regularly occur in profoundly IgG-deficient common variable immunodeficiency (CVID) patients. The isotypes, antigenic targets, and origin(s) of their disease-causing autoantibodies are unclear. Objective To determine reactivity, clonality and provenance of AIC-associated IgM autoantibodies in CVID patients. Methods We utilized glycan arrays, patient erythrocytes, and platelets to determine targets of CVID IgM autoantibodies. Glycan binding profiles were used to identify auto-reactive clones across B cell subsets, specifically circulating marginal zone-like (MZ) B cells, for sorting and IGH sequencing. The locations, transcriptomes and responses of tonsillar MZ B cells to different T helper cell subsets were determined by confocal microscopy, RNA-sequencing, and co-cultures, respectively. Results Autoreactive IgM coated erythrocytes and platelets from many CVID patients with AICs (CVID+AIC). On glycan arrays, CVID+AIC plasma IgM narrowly recognized erythrocytic i antigens and platelet i-related antigens and failed to bind hundreds of pathogen- and tumor-associated carbohydrates. Polyclonal i antigen-recognizing B-cell receptors were highly enriched among CVID+AIC circulating marginal zone (MZ) B cells. Within tonsillar tissues, MZ B cells secreted copious IgM when activated by the combination of IL-10 and IL-21 or when cultured with IL10/IL-21 secreting FOXP3-CD25hiTfh cells. In lymph nodes from immunocompetent controls, MZ B cells, plentiful FOXP3+ regulatory T cells, and rare FOXP3-CD25+ cells that represented likely CD25hiTfh cells, all localized outside of GCs. In CVID+AIC lymph nodes, cellular positions were similar but CD25hiTfh cells greatly outnumbered regulatory cells. Conclusions Our findings indicate glycan-reactive IgM autoantibodies produced outside of GCs may contribute to the autoimmune pathogenesis of CVID.