Transplantation with IL-23^−/− marrow grafts reduces systemic proinflammatory cytokine production. Lethally irradiated Balb/c mice (900 cGy) were transplanted with either BM alone from B6 (n = 21, ▫) or IL-23^−/− (n = 20, ) animals or BM and spleen cells (0.4-0.6 × 10⁶) from B6 (n = 23, ■) or IL-23^−/− animals (n = 22, □). Mice were bled 7 days after transplantation, and serum was assayed for the indicated cytokines using the multiplex cytokine Bio-Rad Laboratories assay system. Data are presented as the mean plus or minus SEM and are derived from 6 independent experiments. *P ≤ .05; **P < .01.