- Human peritoneal mesothelial cells synthesize IL-1α and β. We studied the ability of human peritoneal mesothelial cells (HPMC) to produce the major pro-inflammatory cytokines interleukin-1α (IL-1α) and -β when stimulated by lipopolysaccharide (LPS), tumor necrosis factor α (TNFα) or IL-1α, or combinations of these three factors. Biological activity of IL-1 was measured by bioassay, and levels of IL-1α and -β were determined using specific radioimmunoassays. We found that HPMC are capable of secreting IL-1α and -β in response to stimulation by these substances, but stimulation with a combination of LPS + TNFα, LPS + IL-1α, or TNFα + IL-1α, had a marked synergistic effect on cytokine production. A combination of all three substances together had a significantly enhanced synergistic effect. Using reverse transcription PCR, we found a peak in IL-1α and β mRNA levels three hours after stimulation. We found that LPS, TNFα and IL-1α alone, or in combination, caused an increase in IL-1α and -β mRNA levels. Cycloheximide and actinomycin D blocked the production of IL-1α and -β protein, showing that de novo production of IL-1 or synthesis of mRNA stabilizing proteins are needed after stimulation. We thus conclude that HPMC play an important role in the amplification of the initial peritoneal inflammatory response which originates in the peritoneal macrophages, and these findings are of importance in understanding the peritoneal response to infection in continuous ambulatory peritoneal dialysis (CAPD) patients.