Lineage-specific deletion of p16^INK4a has no effect on lymphocyte development in young mice. (A) Protein expression of p16^INK4a in purified mouse T cells from Lck-Cre p16^+/+ and Lck-Cre p16^L/L mice of indicated ages. Relative quantification of p16^INK4a expression after normalization to tubulin is shown. See supplemental Figure 1 for purification scheme. (B) Protein expression of p16^INK4a in purified B and T cells from CD19^Cre/+p16^L/L and CD19^Cre/+p16^+/+ mice of indicated ages. See supplemental Figure 1 for purification scheme. (C) Comparable thymocyte development in young (6-8 weeks old) Lck-Cre p16^+/+ mice versus young Lck-Cre p16^L/L mice. (Left) Fractions of double-positive, double-negative, and CD4/CD8 single-positive cells. (Right) Fractions of DN1 (CD25⁻CD44⁺), DN2 (CD25⁺CD44⁺), DN3 (CD25⁺CD44⁻), and DN4 (CD25⁻CD44⁻) after Lin⁻CD4⁻CD8⁻ gating. (D) Differentiation of peripheral T cells in young Lck-Cre p16^L/L mice versus Lck-Cre p16^+/+ mice. (Left) CD4⁺ or CD8⁺ SP T-cell percentages in the spleen. (Middle) CD4⁺ memory (CD25⁻CD44^hi) and naive (CD25⁻CD44^lo/−) T-cell fractions from spleen. (Right) CD8⁺ memory (CD25⁻CD44^hi CD122⁺) and naive (CD25⁻CD44^lo/− CD122⁻) T-cell fractions. (E) Development of B-lineage progenitors in bone marrow (BM) in young CD19^Cre/+p16^L/L mice versus CD19^Cre/+p16^+/+ mice. (Left) CD93⁺ immunoglobulin M (IgM)⁻ early B-cell progenitors: pre-pro-B cells, pro-B cells, pre-B cells. (Right) Immature B (Imm-B) cells and mature recirculating B (Recir-B) cells as indicated from mouse bone marrow (BM). (F) Differentiation of splenic B-cell subsets in of young CD19^Cre/+p16^L/L mice versus CD19^Cre/+p16^+/+ mice. Different B-cell subsets are as shown: mature (IgM^loIgD^hi), immature (IgM^hiIgD^lo), transitional 1 (T1, CD21⁻IgM⁺), transitional 2 (T2, IgM^hiIgD^hi), and marginal zone (MZ, CD23⁻CD21⁺B220⁺).