Active Mac-1 (CD11b/CD18) on DCs modulates T-cell activation. (A) DCs (5 × 10⁵/well) were placed into 96-well plates that had been coated with 10 μg/mL ICAM-1–Fc. DCs were left untreated or were preincubated with 5 mM Mg²⁺ or 10 μg/mL of the indicated antibodies for 1 hour. Plates were incubated for 45 minutes at 37°C, and wells were washed 4 times and analyzed for bound cells by microscopy as described in “Materials and methods.” Error bars represent SD of 5 independent experiments. (B) CD3⁺ T cells (BALB/c; 1 × 10⁵/well) were cocultured with allogeneic bmDCs (C57BL/6) at a T/DC ratio of 20:1 for 3 days in 96-well plates. DCs were pretreated with 10 μg/mL anti-CD11b antibody and where indicated 5 mM Mg²⁺ was added. After 3 days of coculture, 1 μCi (0.037 MBq) ³H-thymidine/well was added to the culture for another 18 hours to determine T-cell proliferation. Error bars represent SD of 3 independent experiments.