B- and T-cell development in Artemis-deficient mice. The phenotype of B and T cells was analyzed by flow cytometry in lymphoid organs. Staining antibodies are indicated. Plots were gated on viable (propidium iodide–negative) lymphoid cells. Percentages of cells in the quadrants are given. (A) Analysis of T-cell subsets in thymus, spleen, and blood illustrates an absence of mature CD4⁺ and CD8⁺ cells in Artemis-deficient mice. (B) Analysis of B-cell subsets in bone marrow (BM), blood, and spleen shows a blockade of B-cell development at pro-B–pre-B (B220⁺/IgM⁻) stage in BM (left), leading to an absence of immature and recirculating mature (both B220⁺/IgM⁺) B cells in BM, and of B220⁺/IgM⁺ mature B cells in spleen and blood.