Enhanced killing capacity of human Kupffer cells after activation with human granulocyte/macrophage-colony-stimulating factor and interferon γ

In this study we investigated the effect of the cytokines human granulocyte/macrophage-colony-stimulating Factor (hGM-CSF) and interferon ? (IFN?) on human Kupffer-cell-mediated cytotoxicity against the SW948 coloncarcinoma cell line. Kupffer cells were isolated from small liver wedge biopsies, taken from 14 patient who had had abdominal surgery for colon carcinoma or partial hepatectomy. The cells were incubated with hGM-CSF (100 ng/ml), or with IFN? (100 U/ml) or with their combination and the perecentage cytotoxicity was determined using a recently described modified assay. Additional experiments were performed with tumour-necrosis-factor-a(TNFa)-sensitive U937 cells as target. The TNFa secretion of Kupffer cells was measured and we evaluated the effect of TNFa on colon tumour targets. We performed human-Kupffer cell-mediated cytotoxicity blocking experiments with anti-TNFa and used paraformaldehydefixed Kupffer cells to demonstrate lysis of TNFa-sensitive WEHI-164 cells and of SW948 cells. The overall cytotoxicity against SW948 caused by unactivated Kupffer cells (n=14), and by Kupffer cells activated with hGM-CSF (n=14), IFN? (n=6) or their combination (n=6) was respectively: 19.5±2.6%, 25.3±2.9% 41±9.4% and 45.6±8% at E/T=1 and 28.2±2.9%, 35.6±3.2%, 55.6±9.7% and 62.8% at E/T=5. All differences were statistically significant (P<0.05). No growth-promoting activity by hGM-CSF on the SW948 tumour cells was observed. U937 cells were highly susceptible to Kupffer-cell-mediated cytotoxicity. The TNFa secretion by human Kupffer cells increased in parallel to their cytotoxicity after incubation with these cytokines. Soluble TNFa had only a slight anti-proliferative effect on SW948 cells, while specific anti-TNFa blocked Kupffer cell cytotoxicity by up to 80%. Finally, paraformaldehyde-fixed Kupffer cells were able to lyse WEHI-164 and SW948 cells. This indicates that expression of cell-associated TNFa is the main cytolytic mechanism of human-Kupffer-cell-mediated cytotoxicity. The implications for the use of hGM-CSF and IFN? in vivo are discussed.