Significance of alternatively activated macrophages in patients with intrahepatic cholangiocarcinoma

Many studies have shown that tumor-associated macrophages (TAMs) contribute to tumor development and poor prognosis in various cancers. In this study, we investigated the macrophage populations and phenotypes, and their correlation to angiogenesis, immunosuppression, and clinical prognosis in intrahepatic cholangiocarcinoma (ICC). CD68 (+) and CD163 (+) macrophage infiltration was analyzed in paraffin-embedded tissue samples from 39 patients. CD163 is used as a marker of M2 macrophages. Neovascularization and infiltration of forkhead box P3 (FOXP3) (+) regulatory T cells were also evaluated. The number of CD68 (+) and CD163 (+) macrophages was positively correlated with the numbers of vessels and regulatory T cells. The number of CD163 (+) cells was more closely associated with them. Intrahepatic cholangiocarcinoma (ICC) patients with high counts of CD163 (+) macrophages showed poor disease-free survival (P = 0.0426). The macrophage density was not correlated with overall survival. In an in vitro study using ICC cell lines (HuCCT1, RBE, and MEC) and human macrophages, tumor cell supernatant (TCS) from cell lines induced an activation of signal transducers and activators of transcription-3 (Stat3) and macrophage polarization toward the M2 phenotype. Tumor cell supernatant (TCS) from HuCCT1 most strongly induced Stat3 activation and production of cytokines and other bioactive molecules such as interleukin (IL)-10, vascular endothelial growth factor (VEGF)-A, transforming growth factor (TGF)-beta, and matrix metalloproteinase (MMP)-2. Down-regulation of Stat3 by siRNA significantly suppressed the production of IL-10 and VEGF-A. These results provide suggestive evidence that TAMs contribute to cancer progression via Stat3 activation, and CD163 is useful for evaluating M2 TAMs and predicting the clinical prognosis of ICC patients.