(a) Thymi from the indicated 18 day-old littermates were weighed using an analytical balance and normalised to body weight. Thymocytes were stained with fluorochrome-conjugated antibodies against CD4 and CD8 and analyzed by flow cytometry. Cells were gated for the DP, SP and DN stages and absolute numbers and the indicated ratios determined. (b) Thymocytes from Ptpn2+/+ and Ptpn2−
/− (BALB/c) littermates were stained with fluorochrome-conjugated antibodies against CD4, CD8, TCR-Vβ3, -5, -6 and -8 and analyzed by flow cytometry. Cells were gated for the CD4 and CD8 SP stages and the percentages of TCR-Vβ3, -5, -6 and -8 T cells determined. (c) Thymocytes from the indicated 18 day-old mice were stained with fluorochrome-conjugated antibodies against CD4, CD8, TCRβ and CD69 and analyzed by flow cytometry. Cells were gated for the different developmental stages according to the expression of the positive selection markers TCRβ and CD69. Results in (a–c) are means ± SEM for the indicated number of mice and are representative of at least two independent experiments; significance determined using a two-tailed Mann-Whitney U Test; *p<0.05 ** p<0.01 *** p<0.001.