PBN does not inhibit serum proinflammatory cytokine production. Lethally irradiated (1000 cGy) B6 mice received transplants of B6 BM cells and were then treated with either rat IgG (open bar; n = 6-11/group) or anti-CD40 antibody (8 μg/d) for 4 days beginning on day one after transplantation. Mice treated with anti-CD40 were administered either DMSO (shaded bar; n = 12-18/group) or PBN (solid bar; n = 12-19/group) for 5 days (days 0-4) after BMT. Mice were bled after completion of anti-CD40 administration (day 4) and analyzed for (A) IL-12, (B) IFN-γ, (C) TNF-α, and (D) nitrate/nitrite as described in “Study design.” Data are presented as the mean ± SEM and are the cumulative results from 2 to 4 independent experiments for each cytokine. P < .01, IgG versus DMSO, for IL-12, IFN-γ, TNF-α, and nitrate/nitrite; P = NS, DMSO versus PBN, for IL-12, IFN-γ, TNF-α, and nitrate/nitrite.