Macrophages are one of the immune populations frequently found in colorectal tumors and high macrophage infiltration has been associated with both better and worst prognosis. Importantly, according to microenvironment stimuli, macrophages may adopt different polarization profiles, specifically the pro-inflammatory or M1 and the anti-inflammatory or M2, which display distinct functions. Therefore, concomitantly with the number of tumor-associated macrophages (TAMs), their characterization is fundamental to unravel their relevance in cancer. Here, we profiled macrophages in a series of 150 colorectal cancer (CRC) cases by immunohistochemistry, using CD68 as a macrophage lineage marker, CD80 as a marker of pro-inflammatory macrophages, and CD163 as a marker of anti-inflammatory macrophages. Quantifications were performed by computer-assisted analysis in the intratumoral region, tumor invasive front, and matched tumor adjacent normal mucosa (ANM). Macrophages, specifically the CD163 + ones, were predominantly found at the tumor invasive front, whereas CD80 + macrophages were almost exclusively located in the ANM, which suggests a predominant anti-inflammatory polarization of TAMs. Stratification according to tumor stage revealed that macrophages, specifically the CD163 + ones, are more prevalent in stage II tumors, whereas CD80 + macrophages are predominant in less invasive T1 tumors. Specifically in stage III tumors, higher CD68, and lower CD80/CD163 ratio associated with decreased overall survival. Importantly, despite the low infiltration of CD80 + cells in colorectal tumors, multivariate logistic regression revealed a protective role of these cells regarding the risk for relapse. Overall, this work supports the involvement of distinct microenvironments, present at the intra-tumor, invasive front and ANM regions, on macrophage modulation, and uncovers their prognostic value, further supporting the relevance of including macrophage profiling in clinical settings.

In order to improve the efficacy of conventional radiotherapy, attention has been paid to immune cells, which not only modulate cancer cell response to therapy but are also highly recruited to tumours after irradiation. Particularly, the effect of ionizing radiation on macrophages, using therapeutically relevant doses, is not well understood. To evaluate how radiotherapy affects macrophage behaviour and macrophage-mediated cancer cell activity, human monocyte derived-macrophages were subjected, for a week, to cumulative ionizing radiation doses, as used during cancer treatment (2 Gy/fraction/day). Irradiated macrophages remained viable and metabolically active, despite DNA damage. NF-kappaB transcription activation and increased Bcl-xL expression evidenced the promotion of pro-survival activity. A significant increase of pro-inflammatory macrophage markers CD80, CD86 and HLA-DR, but not CCR7, TNF and IL1B was observed after 10 Gy cumulative doses, while anti-inflammatory markers CD163, MRC1, VCAN and IL-10 expression decreased, suggesting the modulation towards a more pro-inflammatory phenotype. Moreover, ionizing radiation induced macrophage morphological alterations and increased their phagocytic rate, without affecting matrix metalloproteases (MMP)2 and MMP9 activity. Importantly, irradiated macrophages promoted cancer cell-invasion and cancer cell-induced angiogenesis. Our work highlights macrophage ability to sustain cancer cell activities as a major concern that needs to be addressed to improve radiotherapy efficacy.

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