VIP fails to modulate spontaneous IL-10 and TNF-α production by RA-SMCs. RA-SMCs were plated out at 2 × 105 cells per well in a flat-bottomed 96-well plate and treated with VIP (a,b) or PDE-resistant dibutyryl cAMP (c,d) for 24 hours at 37°C in a 5% CO2 humidified atmosphere, after which time supernatants were harvested and assayed for spontaneous production of IL-10 (a,c) and TNF-α (b,d) by ELISA. Data are mean cytokine levels in pg/ml of triplicate culture supernatants ± SD, showing a representative (one patient) of n = 3 replicate experiments for a total of four patient samples. *P < 0.05. PDE, phosphodiesterase; RA-SMC, rheumatoid arthritis synovial membrane cell; VIP, vasoactive intestinal peptide.