DTT primes activated human T cells for Gal-1–induced PS exposure. (A) PHA-activated T cells were incubated with RPMI alone, 10 μM Gal-1 alone, or with the respective concentration of DTT with or without 10 μM Gal-1 for 9 hours as indicated, followed by the detection for PS exposure. (B) HL60 cells were treated with either freshly prepared C2S-Gal-1 or C2S-Gal-1 incubated for 24 hours in the absence of DTT. Following C2S-Gal-1 addition, cells were incubated for 4 hours followed by analysis for PS exposure. (C) PHA-activated T cells or MOLT-4 cells were incubated with 10 μM Gal-1 or 10 μM C2S-Gal-1 with or without 1.2 mM DTT for 9 hours, followed by detection for PS exposure. (D) PHA-activated T cells or MOLT-4 cells were incubated with 10 μM C2S-Gal-1 with or without 30 mM TDG as indicated for 9 hours followed by detection for PS exposure. Error bars represent the standard deviation of duplicate samples.