Activation, localization, and autoantibody production of tissue-based age-associated B cells in human type 1 diabetes

Introduction/Rationale: T cells mediate type 1 diabetes (T1D) pathogenesis, but mouse studies indicate that B cells function as critical antigen presenters. The specific B cells that contribute to disease in humans are poorly defined because studies typically sample blood.

Methods: We profiled B cells and their antibody genes in lymphoid tissues (spleen, pancreatic and mesenteric lymph nodes) of T1D organ donors (n=23) and controls (n=19) from the Human Pancreas Analysis Program. We performed phenotyping, single cell RNA sequencing, antibody gene sequencing, and in vitro stimulation to identify B cell signatures associated with T1D.

Results: We observed an increase in age-associated B cells (ABCs; IgD-IgM-CD21-CD11c+Tbet+) in multiple lymphoid tissues during T1D, most strikingly in male spleen. RNA sequencing of sorted ABCs from spleens of 7 age- and sex-matched T1D/control pairs identified T1D-associated transcriptional changes: T1D ABCs upregulated genes including LAIR2, ROR1, and RAMP1 and downregulated MYC and EGR3. TNFRSF1B (TNF receptor 2) and downstream signaling components were upregulated in a subset of ABCs in T1D males, consistent with increased cell activation and survival. Stimulated ABCs from T1D donors also harbored reactivity to T1D-associated autoantigens (insulin, IA-2, GAD65). Antibody clone tracking revealed clonal sharing between splenic ABCs and multiple antigen-experienced B cell subsets in pancreatic lymph nodes (pLN), suggesting these pLN clones may originate in spleen. Monoclonal antibodies generated from these shared pLN/spleen ABC clonal lineages demonstrated both T1D autoantigen binding and multireactivity.

Conclusion: These findings support a novel role for ABCs in T1D. Our data suggest that expanded autoreactive ABC reservoirs in spleen can seed effector B cell populations in pLN, where T1D autoimmune responses likely occur. These findings identify new mechanisms for the contribution of tissue-based B cells to T1D pathogenesis and have implications for B cell therapeutic targeting.