AIM: To investigate the importance of direct contact between Kupffer cells (KCs) and hepatocytes (HCs) during hepatic inflammatory responses, and the effect of leflunomide′s active metabolite, A771726, on cytokines in KCs, HCs and KC cocultures (DC cocultures).METHODS: KCs and HCs in liver were isolated by digestion with pronase and collagenase. Lipopolysaccharide (LPS)-induced inflammatory response in monocultures of rat HCs and KCs was compared with that in DC cocultures. Tumor necrosis factor-α (TNF-α) and interleukin-1 (IL-1)concentrations in different culture supatants were measured with ELISA. TNF-α mRNA in KCs of inflammatory liver injury was analyzed with reverse transcriptase polymerase chain reaction (RT-PCR).RESULTS: DC cocultures strongly exhibited the production of TNF-α and IL-1 compared with other cultures, and these cytokines were mainly produced by KCs, especially by activated KCs. Time course studies revealed an increased production of TNF-α preceding the IL-1 production,suggesting that increased TNF-α levels could be involved in the increase of IL-1 production. Leflunomide′s active metabolite, A771726, had significantly inhibitory effect on TNF-αand IL-1 at protein and transcription levels, and the reduced production of IL-1 by A771726 was associated with the inhibitory action of A771726 on TNF-α.