Constitutive ST3Gal-I transgene expression in T-cell ontogeny and peripheral T-lymphocyte homeostasis. (A) ST3Gal-I transgene construct. The EcoRI fragment of human ST3Gal-I cDNA was inserted into the VA hCD2 minigene cassette, which contains the human CD2 promoter sequence. E, EcoRI; K, KpnI; X, XbaI. (B) Thymic tissue sections from ST3Gal-ITg animals and wild-type littermates reveal a loss of PNA ligands in both thymic cortex (C) and medulla (M) as a result of constitutive ST3Gal-I expression in T cells. (C) Total thymocyte subset numbers and frequencies among CD4/CD8 double-positive (DP), double-negative (DN), and SP T cells in ST3Gal-ITg and wild-type littermate mice. (D) TCR Vβ repertoire expression in ST3Gal-ITg and wild-type littermate CD8 SP thymocyte populations. (E) Analysis by flow cytometry indicates decreased PNA ligands on ST3Gal-ITg cells compared to littermate control cells among total thymocytes, CD8 SP thymocytes, and CD8+ T cells from spleen. (F) Total cell and CD8+ T-cell numbers in spleen and lymph nodes in ST3Gal-ITg and wild-type littermate animals. Data are presented as means ± standard errors of the means (n = 6). , statistically significant difference from wild-type littermates (P < 0.05, paired t test).