VIP suppresses LPS induction of monocyte TNF-α but has no effect on IL-10 production. Fresh, elutriated human monocytes were plated out at 2 × 105 cells per well in a U-bottomed 96-well plate and pretreated with VIP (a,b), rolipram (c,d), or dibutyryl cAMP (e,f) for 1 hour prior to stimulation with 1 ng/ml LPS and incubated for 24 hours at 37°C in a 5% CO2 humidified atmosphere, after which time supernatants were harvested and assayed for TNF-α and IL-10 by ELISA. Data are mean cytokine levels in pg/ml of triplicate culture supernatants ± SD, showing a representative of n = 4 replicate experiments. *P < 0.05; **P < 0.01; ***P < 0.001. LPS, lipopolysaccharide; TNF-α, tumour necrosis factor α; VIP, vasoactive intestinal peptide.