Suppressor cytokine expression in carbon tetrachloride-induced liver injury, Kupffer cells and human liver disease

Hepatic macrophages, or Kupffer cells (KC), play a central role in the generation of inflammation in the liver, both in animal models and human liver disease. The suppressor cytokine interleukin (IL)-10, produced by monocytes, macrophages and lymphocytes, has profound inhibitory and autoregulatory effects on macrophage function and are likely, therefore, to be important in the regulation of inflammation. In this study, we examined the expression of IL-10 protein in human liver, and IL-10 and IL-13 mRNA in vivo, in carbon tetrachloride-induced liver injury and in vitro, in LPS-stimulated KC in comparison to the pro-inflammatory cytokine, IL-1 beta. Human liver samples, obtained by percutaneous biopsy or at transplantation, were homogenized with protease inhibitors and IL-10 protein quantified by ELISA. Rats were injected with CCL4 (1 ml/kg) and sacrificed at 0, 6, 24, 48 and 72 hours (n = 2). Normal rat KC were isolated by pronase-collagenase perfusion and centrifugal elutriation, and stimulated with LPS (1 ug/ml, 0, 2, 4, 6, 8, 24, 48 and 72 hours, n = 4). Total RNA (1 ug) from rat liver and KC was subjected to RT-PCR for IL-10, IL-13 and IL-1 beta and PCR products semi-quantified by densitometry. IL-10 protein was found at very low levels in only 4 of 66 human liver samples. IL-10 and IL-13 mRNAs were upregulated as early as 6 hours after CCl4, persisting for 72 hours and concurrent with IL-1 beta expression. Both IL-10 and IL-1 beta mRNAs were detectable in unstimulated KC, and were again upregulated early after LPS (at 2 hours), reaching a maximum 4 - 6 hours after activation. In conclusion, levels of IL-10 protein are low in human liver, but early increased transcription of suppressor cytokines has been demonstrated, both in stimulated KC and in experimentally-induced liver injury in rats during initiation of the inflammatory response. The balance of pro-inflammatory and suppressor cytokine responses may be important in determining KC activation and subsequent hepatic inflammation.