Figure 1

Depletion of macrophages inhibits tumour development. On day 1, mice were i.p. injected with a lethal dose of AC29 mesothelioma tumour cells and were treated twice with liposome-encapsulated clodronate (macrophage depletion) or liposome-encapsulated PBS (control) on days 5 and 10 after tumour injection (n=10). Twelve days after tumour injection, mice were killed and tumour weight was measured. All visible tumour material was excised from each mouse and data are expressed as wet weight (accuracy of 0.001 g). FACS analysis was performed to verify the effectiveness of macrophage depletion using liposome-encapsulated clodronate. Tumour biopsies were embedded in Tissue-Tek II and snap frozen in liquid nitrogen. Tissue sections (6 μm) were analysed for the presence of macrophages. (A) Effect of macrophage depletion on tumour growth. Tumour growth was observed in all five mice treated with control liposomes; in contrast, only two out of five mice treated with macrophage-depleting liposomes developed visible tumour growth on day 12. Significant reduction in the percentage of F4/80⁺MHCII⁺ cells was found in the peritoneal cavity of macrophage-depleted mice (P=0.0015). Tumour weight was found to be lower in macrophage-depleted animals (P=0.077). (B) TAMs in murine mesothelioma. Tumour biopsies of control-treated mice showed infiltration of F4/80⁺ and CD206⁺ cells (magnification: upper, × 200; lower, × 400). ^**P<0.001.