T-cell development in SOCS1-deficient mice is skewed toward CD8 lineage. (A) Thymocytes from 8-day-old SOCS1^-/-IFNγ^+/+ and 4-week-old SOCS1^-/-IFNγ^-/- mice and their respective controls were stained for CD4 and CD8. Numbers within each quadrant represent the frequency of thymocytes in DN, DP, CD4⁺, or CD8⁺ stages of development. Data shown are representative of several independent experiments. (B) CD8⁺ SP cells in SOCS1-deficient thymus are mature T cells. Thymocytes from 4-week-old SOCS1^-/-IFNγ^-/- mice and their littermate controls were stained for TCR-β, CD4, and CD8, and the distributions of DN, DP, CD4⁺, and CD8⁺ cells within TCR^lo/int and TCR^hi populations were estimated. Frequency of TCR^hi cells is indicated within histograms, and numbers within the quadrants denote the percentages of each subset within TCR^lo/int and TCR^hi populations. Representative data from at least 4 animals per group are shown. (C) Increased CD44 expression on CD8⁺ SP cells in SOCS1^-/-IFNγ^-/- thymus. Expression of CD44 on CD8⁺ and CD4⁺ SP thymocytes from SOCS1^-/-IFNγ^-/- mice and their littermate controls is shown as histograms. Percentage of positive cells within the marker boundary is indicated. (D) SOCS1 is not a critical regulator of pre-T-cell development during the DN stage. Thymocytes from 4-week-old SOCS1^-/-IFNγ^-/- mice and their littermate controls were stained with biotinylated anti-CD4, anti-CD8, anti-CD25-PE, and anti-CD44-FITC, followed by ST-SPRD. Surface expression of CD25 and CD44 on gated CD4^-CD8^- DN cells is shown as dot plots. Percentages of cells within the 4 DN developmental stages are indicated. Results shown are representative of at least 3 animals per group from 2 experiments.