IL-12 p40 production by normal and c-Rel–deficient cells. DC-enriched APCs from spleen (a) and bone marrow (b); and microglia (c) and astrocytes (d) from brain and spinal cord were prepared as described in Methods. All cells were cultured at 10⁶/ml with or without 1 μg/ml (for spleen and bone marrow APCs) or 5 μg/ml (for microglia and astrocytes) LPS. Culture supernatants were collected at 40 hours and IL-12 concentrations were determined by ELISA. Results are representative of two experiments.