Intratumoural expression of IL-6/STAT3, IL-17 and FOXP3 immune cells in the immunosuppressive tumour microenvironment of colorectal cancer Immune cells-positive for IL-6, STAT3, IL-17 and FOXP3 and colorectal cancer development

Abstract

Immune cells in the tumour microenvironment (TME) interact with each other and with tumour cells to promote tumour development. IL-6/STAT3 pathway induces and maintains mainly pro-tumour TME. Macrophages and lymphocytes are positive for IL-6, STAT3 and IL-17, while FoxP3 cells are mainly regulatory cells. IL-17+ and FoxP3+ immune cells have impact on gut inflammation and tumourigenesis. The aim of this study was to determine IL-6+, STAT3+, IL-17+ and FoxP3+ immune cells in colorectal cancer (CRC) TME and explore their association with clinicopathological parameters and mismatch repair (MMR) status. The investigated samples were collected from 104 CRC patients. Immunohistochemistry for the aforementioned markers and microsatellite instability (MSI) markers was performed. MSI testing was used. The investigated immune cells were significantly more in the invasive front (IF) as compared to tumour stroma (TS). IL-6+ and STAT3+ immune cells were more in the early tumour stages as compared to advanced stages. IL-17+ and IL-6+ immune cells were more in well and moderately differentiated cancers. IL-6+, STAT3+ and IL-17+ immune cells prevailed in the TME in microsatellite stable patients and only FoxP3+ cells were fewer there. Higher numbers of STAT3+ cells correlated with longer survival. These results support the suggestion that the transition of normal colonic mucosa to CRC is marked by a shift of Th programme, leading to accumulation of Th17 cells and Tregs that sustain tumour cell growth through the IL-6/STAT3 signalling pathway.