Impaired CpG Demethylation in Common Variable Immunodeficiency Associates With B Cell Phenotype and Proliferation Rate

Common Variable Immunodeficiency(CVID) is characterized by impaired antibody production and poor terminal differentiation of the B cellcompartment, yet its pathogenesis is still poorly understood. We first reported the occurrence of epigenetic alterations in CVID by high-throughput methylation analysis in CVID-discordant monozygotic twins. Data from a recent whole DNA methylome analysis throughout different stages of normal B celldifferentiation allowed us to design a new experimental approach. We selected CpG sitesfor analysis based on two criteria: one, CpGs with potential association with the transcriptional status of relevant genes for B cellactivation and differentiation; and two, CpGs that undergo significant demethylationfrom naive to memory B cellsin healthy individuals. DNA methylation was analyzed by bisulfite pyrosequencingof specific CpG sitesin sorted naive and memory B cellsubsets from CVID patients and healthy donors. We observed impaired demethylationin two thirds of the selected CpGs in CVID memory B cells, in genes that govern B cell-specific processes or participate in B cellsignalling. The degree of demethylationimpairment associated with the extent of the memory B cellreduction. The impaired demethylationin such functionally relevant genes as AICDA in switched memory B cellscorrelated with a lower proliferative rate. Our new results reinforce the hypothesis of altered demethylationduring B celldifferentiation as a contributing pathogenic mechanism to the impairment of B cellfunction and maturation in CVID. In particular, deregulated epigenetic control of AICDA could play a role in the defective establishment of a post- germinal center B cellcompartment in CVID.