TNFα inhibits expression of IL-12/IL-23 p40. Thioglycolate-elicited macrophages were cultured in the presence or absence of 30 or 100 ng/ml TNFα for 8 h and then stimulated for a further 18 h with 1 ng/ml LPS. (A–C) Levels of p40, IL-1β, and IL-6 protein were determined in the culture supernatants by ELISA. (D) Relative levels of p40 mRNA from WT, p55 TNFR^−/−, and p75 TNFR^−/− LN cells 14 d after immunization were determined by real time PCR. Histograms show mean ± SEM (n = 4). *, P < 0.05; **, P < 0.01; ***, P < 0.001.