Responses of CD4⁺ T cells from WT or gene-deficient donors to host stimulator cells in the MLR. Panel A shows means ± SEM of ³H-thymidine incorporation of triplicate cultures of donor T cells at 72 (▥), 96 (▦), and 120 hours (▪). Panel B shows mean ± SEM concentrations of IFNγ (▥), IL-2 (▪), and TNF-α (▦) in the supernatants of triplicate MLR cultures at 60 hours. Background ³H-thymidine incorporation was less than 3000 cpm with syngeneic stimulator cells, and background cytokine concentrations were less than 100 pg/mL IL-2. Results are representative of at least 3 MLR cultures.