Gene expression comparison, WT and PDAP1-deficient primary B lymphocytes

Class switch recombination (CSR) and somatic hypermutation (SHM) are antibody gene diversification reactions occurring in mature B cells that are essential for protective humoral immunity. CSR and SHM are initiated following activation by the antigen, and are dependent on efficient induction of activation-induced cytidine deaminase (AID). Therefore, mature B cell viability and fitness are crucial to mount effective immune responses. Here, we identified PDGFA-associated protein 1 (Pdap1) as an essential regulator of cellular homeostasis in mature B cells. Pdap1 deficiency leads to sustained expression of the integrated stress response (ISR) effector activating transcription factor 4 (Atf4) and induction of the ISR transcriptional program, increased cell death, and defective AID expression. As a consequence, loss of Pdap1 reduces germinal center B cell formation and impairs CSR and SHM. Thus, Pdap1 protects mature B cells against chronic ISR activation, and ensures efficient antibody diversification by promoting their survival and optimal function. Overall design: Two conditions were tested: stimulation with LPS and IL-4 (to induce CSR to IgG1) or LPS, BAFF and TGFbeta (to induce CSR to IgG2b). Samples were harvested from control and Pdap1F/FCd19Cre/+ splenocyte cultures 48 h after stimulation. Three biological replicates (= mice) per sample were employed for the analysis (control mice: C1 to C3; Pdap1F/FCd19Cre/+ mice: P1 to P3).