Cytokines in cyst fluids from polycystic kidneys. We sought evidence of cytokine presence and interleukin-1β (IL-1β) bioactivity in 104 aerobic culture negative cyst fluids (CFs) from 13 kidneys of 13 patients with symptomatic normal to end-stage autosomal dominant polycystic kidney disease (ADPKD). ELISAs were used to detect IL-1β, interleu-kin-2 (IL-2), tumor necrosis factor alpha (TNFα) and stromelysin. Prostaglandin E₂ (PGE₂) was detected by radioimmunoassay. IL-1 β was present in 65 of 94 (<20 to 419 pg/ml, TNFα in 54 of 75 (<10 to 73 pg/ml), stromelysin in 18 of 23 (<1.0 to 56 ng/ml), IL-2 in 7 of 23 (0.1 to 1.3 ng/ml) and PGE₂ in 9 of 10 fluids (0.03 to 0.49 ng/ml). Of 51 fluids with immunoreactive IL-1/3, 36 were mitogenic for thymocytes. IL-1β concentrations correlated directly with those of IL-2; IL-1β presence was associated with higher stimulation indices, higher mean concentrations of TNFα, IL-2, stromelysin, and PGE₂, and with positive endotoxin assays, suggesting activation of the cytokine cascade in vivo. Cytokine, stromelysin and PGE₂ concentrations did not correlate with sodium or non-sodium solute concentrations, nor with CF blood, osmolality, or endotoxin activity, indicating that differences in concentrations among fluids could not be explained by differences in water content. These data identify cytokines as candidate contributors to the morbidity and pathogenesis of ADPKD.