The DNA methylomes of hyper-IgM syndrome type 2 B cells provide insights into the roles of activation-induced deaminase prior to the germinal center reaction

Inactivating mutations in activation induced deaminase (AID) lead to hyper-IgM syndrome type 2 (HIGM2), a rare primary antibody deficiency. AID-mediated cytosine deamination has been proposed as mediating active demethylation, although there is evidence both to support and cast doubt on such a role. We here made use of HIGM2 B cells to investigate direct AID involvement in active DNA demethylation. HIGM2 naïve and memory B cells both display widespread DNA methylation defects. For genes that undergo demethylation in the transition from naïve to memory B cells but not in HIGM2 individuals, we did not observe AID involvement but a participation of TET enzymes. DNA methylation alterations in HIGM2 naïve B cells are related to premature overstimulation of the B-cell receptor prior to the germinal center reaction. Our data supports a role for AID in B cell central tolerance in preventing the expansion of autoreactive cell clones, affecting the correct establishment of DNA methylation patterns without involvement of its cytosine deaminase activity. Overall design: Tagmentation-based whole-genome bisulfite sequencing of naïve (NBC) and non-class-switched memory B cells (ncsMBC) of two HIGM2 patients and two controls