Restoration of SHM and CSR by complementation with expression of AID variants. (A) Cartoon representation of retroviral constructs of AID variants. (B) Flow cytometry assessing CSR in AID-deficient spleen cells stimulated with IL-4 and LPS and infected with retroviruses-expressing FL or alternatively spliced AID variants. CSR was measured by the number of YFP-positive cells acquiring IgG1 cell surface expression in the gated viable population. Numbers indicate percentage of IgG1⁺GFP⁺ cells (top right). Dot-plot data are representative of 4 individual experiments that are summarized in the bar-chart panel. The P values were obtained using a 1-tailed t test. (C) Flow cytometry assessing SHM activity by scoring GFP reversion frequencies. Murine 70Z/3 cells stably expressing a GFP transgene with a premature stop codon were infected with retroviruses expressing FL or alternatively spliced AID variants. SHM activity was measured by the number of YFP (Y axis) positive cells acquiring GFP (X axis) expression over 6 weeks of time. Numbers indicate the percentage of YFP⁺GFP⁺ cells (top right). Dot-plot data are representative of 4 individual experiments which are summarized in the bar-chart panel. The P values were obtained using a 1-tailed t test.