Macrophage infiltration correlates with tumor stage and angiogenesis in human malignant melanoma: Possible involvement of TNFα and IL-1α

Abstract

We examined whether macrophage infiltration is associated with angiogenesis in cutaneous melanoma. The numbers of macrophages and microvessels increased significantly with increasing depth of tumor and with tumor angiogenesis. Macrophage infiltration thus appeared to provide a useful diagnostic marker for the progression of cutaneous melanoma. We further examined whether human melanoma cells produce angiogenic factors in response to macrophage-derived cytokines, tumor necrosis factor alpha (TNFalpha) and interleukin-1 alpha (IL-1alpha). Treatment of melanoma cells with TNFalpha and IL-1alpha in vitro enhanced the production of interleukin-8 (IL-8) and vascular endothelial growth factor (VEGF), and of basic fibroblast growth factor (bFGF) to a lesser degree, in human melanoma cells. Lipopolysaccharide (LPS)-activated human monocytes enhanced production of IL-8, VEGF, TNF alpha, as well as IL-1alpha, but not bFGF. Co-culture of human monocytes and human melanoma cells was also found to significantly enhance production of IL-8 and VEGF in the absence and presence of LPS, compared with either monocytes or melanoma cells alone. The production of IL-8 and VEGF from co-cultured melanoma cells and LPS-activated monocytes was blocked when anti-TNF-alpha antibody or anti-IL-1alpha antibody was co-administrated. This is direct evidence that production of the potent angiogenic factors IL-8 and VEGF from melanoma cells is up-regulated through TNFalpha and/or IL-1alpha secreted by activated monocytes/macrophages, influencing both tumor growth and angiogenesis in melanomas.