Conditional Artemis deletion in mature B cells. (A) PCR analysis of Artemis deletion. Art^fl and Art^Δ alleles were amplified from genomic DNA from liver, purified splenic mature B cells, and thymocytes from Art^fl/− expressing Cre (+) or not (−) using a combination of primers 1, 3, and 5 (depicted in Figure 1B). (B) Quantification of the Artemis deletion in mature B cells. PCR products from panel A were quantified using ImageJ to calculate the ratio between the Art^fl and the Art^Δ alleles. B cells expressing the Cre recombinase show a 74% deletion of the Art^fl allele. In all the other situations, the ratio between the 2 alleles is approximately 1:1. (C) Analysis of splenic B-cell subpopulations on Artemis deletion. The phenotype of B-cell subpopulations was analyzed by flow cytometry in spleen. Staining antibodies are indicated. Plots were gated on viable (propidium iodide–negative) IgM⁺ lymphoid cells. Percentages of cells in the quadrants are given. T1 indicates transitional type 1 B cells (IgM⁺/CD21⁻/CD23⁻); T2, transitional type 2 B cells (IgM⁺/CD21⁺/CD23⁺); MZ, marginal zone B cells (IgM⁺/CD21⁺/CD23⁻); and M, mature follicular B cells (IgM⁺/CD21^low/CD23⁺).