Endotoxin stimulates interleukin-6 production by human Kupffer cells

Interleukin-6 (IL-6) induces acute-phase protein synthesis in human hepatocytes. We evaluated whether the contiguous hepatic macrophages, human Kupffer cells (HKC), produce IL-6 in response to an inflammatory stimulus. HKC were harvested from collagenase-digested normal liver biopsies and purified (greater than 95% by phagocytosis) by adherence. Following overnight culture, 5 x 10(5) HKC were repleted with fresh media with or without 2.5 micrograms/ml of endotoxin (LPS). Parallel cultures contained polymyxin-B (10 micrograms/ml) or antihuman-IL-6 antibody (4 units/ml). Timed supernatants were collected and IL-6 levels (ng/ml) measured (B9.9 proliferative bioassay). Data analysis was by the paired Student's t test. Unstimulated HKC produced negligible IL-6 levels (less than 0.150 ng/ml). Endotoxin invoked early and sustained HKC production of IL-6, which was completely (P less than 0.001) abrogated by the addition of the anti-IL-6 antibody. Polymyxin B, an LPS-inhibitor, also blocked (P less than 0.001) IL-6 production, indicating the specificity of the response to the inflammatory stimulus. This is the first evidence that HKC can produce IL-6 in response to LPS. Local intrahepatic production of IL-6 may provide a necessary paracrine signal for HKC to amplify directly neighboring hepatocyte acute-phase responses during inflammation in man.