Macrophage-colony stimulating factor (M-CSF)-primed monocyte-derived macrophages, plated at 1 × 105 cells/well, were stimulated with 1 ng/ml LPS in the presence or absence of 10-6M VIP. TNF-α modulation of VIP regulation of IL-10 production was assessed by addition of 10 μg/ml neutralising anti-TNF-α (A2) or 10 ng/ml TNF-α. Results with an isotype-matched control antibody did not differ significantly from the control sample presented in this table. The resulting cultures were incubated for 24 hours at 37°C in a 5% CO2 humidified atmosphere, after which time supernatants were harvested and assayed for IL-10 by ELISA. Data are mean IL-10 levels in pg/ml and percentage suppression by VIP in parentheses of triplicate culture supernatants ± SD, showing a representative of n = 3 experiments. LPS, lipopolysaccharide; TNF-α, tumour necrosis factor α; VIP, vasoactive intestinal peptide.