Rapamycin and anti-CD28 mAb reduce serum levels of inflammatory cytokines. Lethally irradiated (1000 cGy) B10.BR recipients were given transplants of 15 × 10⁶ T-cell–depleted marrow cells from B6 donors plus 15 × 10⁶ splenocytes from B6.Ly5.1 donors or marrow alone. Recipients of marrow and splenocytes were treated intraperitoneally with either control solvent (ctrl.), anti-CD28 mAb at 100 μg × 1 day (αCD28), rapamycin at 1.5 mg/kg × 14 days (rapamycin) or the combination of both (αCD28 + rapamycin). Serum cytokine levels were drawn on day 14. Asterisks denote significant differences compared with control treatment. Groups contained 3 to 4 recipients. Data are displayed as means ± SD and are representative of 2 replicate experiments.