Receptor-activator of NFκB ligand (RANKL) pretreatment impairs IFN-γ-induced nitric oxide (NO) production in a dose-dependent manner. (a) RAW cells were treated as in Figure 2a, and supernatants assayed for NO production on day 4. NO production was significantly inhibited by pretreatment with RANKL (*P < 0.01 versus the IFN-γ only group). (b) RAW cells were grown in the presence of various doses of RANKL, then supplemented with various doses of IFN-γ and maximal GST-RANKL (200 ng/ml) on day 2. NO was assayed on day4. Black bars indicate cells treated on day 2 with 100 ng/ml IFN-γ. (c) This group (indicated by black bars) with statistics. Inhibition of NO production by RANKL pretreatment is dose dependent, with more inhibition with higher doses of RANKL (*P < 0.05 versus 0 ng/ml RANKL).