Stimulation of CD4+ T cells by macrophages presenting OVA in [3H]-thymidine incorporation assays. Isolated macrophages and dendritic cells (DCs) were loaded with OVA (10 μg/ml) and irradiated; then co-cultured with DO11.10 CD4+ T cells for 48 hours. Cultures were then pulsed with [3H]-thymidine, and incorporated counts determined. DCs were used as positive control. Data are the mean ± SEM from three separate experiments.