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

In this study we investigated the effect of the cytokines human granulocyte/macrophage-colony-stimulating Factor (hGM-CSF) and interferon gamma (IFN gamma) on human Kupffer-cell-mediated cytotoxicity against the SW948 colon carcinoma cell line. Kupffer cells were isolated from small liver wedge biopsies, taken from 14 patients who had had abdominal surgery for colon carcinoma or partial hepatectomy. The cells were incubated with hGM-CSF (100 ng/ml), or with IFN gamma (100 U/ml) or with their combination and the percentage cytotoxicity was determined using a recently described modified assay. Additional experiments were performed with tumour-necrosis-factor-alpha (TNF alpha)-sensitive U937 cells as target. The TNF alpha secretion of Kupffer cells was measured and we evaluated the effect of TNF alpha on colon tumour targets. We performed human-Kupffer-cell-mediated cytotoxicity blocking experiments with anti-TNF alpha and used paraformaldehyde-fixed Kupffer cells to demonstrate lysis of TNF alpha-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 gamma (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 TNF alpha secretion by human Kupffer cells increased in parallel to their cytotoxicity after incubation with these cytokines. Soluble TNF alpha had only a slight anti-proliferative effect on SW948 cells, while specific anti-TNF alpha 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 TNF alpha is the main cytolytic mechanism of human-Kupffer-cell-mediated cytotoxicity. The implications for the use of hGM-CSF and IFN gamma in vivo are discussed.