Inactivation of CD11b/CD18 (Mac-1) on macrophages enhances T-cell proliferation. (A-B) Macrophages from bone marrow of CD18^+/+ and CD18^−/− mice were generated as described in “Materials in methods.” Then, 5 × 10⁵ macrophages/well were preincubated with 10 μg/mL anti-CD11a, -b, or -c antibodies and placed into 96-well plates that had been coated with 10 μg/mL recombinant ICAM-1–Fc. Cells were incubated for 45 min at 37°C, washed 4 times, and analyzed for bound cells by microscopy as described in “Materials and methods.” One representative of 3 experiments is shown. Error bars represent SEM of triplicates. (C) CD3⁺ T cells (1 × 10⁵/well) were cocultured with allogeneic macrophages at the indicated T cell–macrophage ratios. Macrophages were left untreated or preincubated with 20 μg/mL anti-CD11b antibody for 2 hours. After 5 days of coculture, 1 μCi (0.037 MBq) of ³H-thymidine/well was added for another 18 hours and T-cell proliferation was assessed. One representative experiment of 3 is shown. Error bars represent SD. (D) CD4⁺ T cells (1 × 10⁵/well) were cocultured with allogeneic CD18^+/+ or CD18^−/− macrophages in the presence of 10 ng/well soluble αCD3 for 4 days, and proliferation was determined by ³H-thymidine incorporation. Proliferation of αCD3-stimulated T cells alone was always less than 1000 cpm. One experiment of 3 is shown. Error bars represent SEM of triplicates.