IFN-γ production by freshly isolated lung macrophages from naive IL-12–/– mice. Pulmonary macrophages were isolated and cultured under different conditions. The supernatants collected at 72 h were measured for IFN-γ by ELISA. (a) Cells cultured with or without LPS (1.6 μg/ml) or live BCG (50 CFU/cell). (b) Cells cultured with 20 pg/ml, 200 pg/ml, or 2 ng/ml of IL-12 alone or together with 1.6 μg/ml of LPS or 50 CFU/cell of live BCG. (c) Cells stimulated with 400 μg/ml of OVA, DBCG (50 CFU/cell), or 8 μg/ml of PPD alone or together with 200 pg/ml of IL-12. The results are expressed as the means of duplicate samples and are representative of three to four independent experiments. OVA, ovalbumin; DBCG, heat-killed BCG.