Effect of IL-6 on tumor cell invasion of vascular endothelial monolayers

The effect of interleukin-6 (IL-6) on the invasive capacity of B16-F1 mouse melanoma cells into vascular endothelial monolayers was examined, and an in vitro assay system for the quantitative determination of tumor cell invasiveness, using confocal microscopy with a fluorescence image analyzer, was developed. First, the invasive capacity of B16-F1 mouse melanoma cells against bovine vascular endothelial monolayers was estimated; then, the gap junctional intercellular communication (GJIC) of endothelial cells was examined. Treatment of endothelial cells with IL-6 resulted in a remarkable increase in the invasion of tumor cells into the endothelial monolayer, which was found to be significant from 25 ng/ ml, and peaked at levels of more than 50 ng/ml. This stimulatory effect of IL-6, which was observed from 3 h after the initiation of treatment and lasted for up to 24 h, was abolished by the addition of the anti-IL-6 antibody. Although phase-contrast microscopy did not reveal any morphological changes in the endothelial cells following treatment with 25-200 ng/ml IL-6 for 24 h, the GJIC was observed to be significantly decreased. These findings indicate that the invasive capacity of tumor cells into endothelial cells is affected by IL-6.