Interleukin-6-Positive Immune Cells as a Possible New Immunologic Marker Associated With the Colorectal Cancer Prognosis.

Chronic inflammation creates tumor microenvironment (TME) that facilitates colorectal cancer (CRC) cell proliferation, migration, metastasis, and tumor progression. Interleukin-6 (IL-6) is a proinflammatory cytokine with a pleiotropic effect on CRC development. We aimed to evaluate IL-6 expression in tumor cells and in immune cells in TME, to assess the serum level and IL6 -174 G/C genotype distribution and to correlate the results with selected morphologic and clinical parameters that may add useful information in understanding the mechanisms of human CRC progression. A total of 153 patients with CRC were recruited in the current study. We assessed the IL-6 serum concentration through the ELISA method, the expression of IL-6 in tumor and in immune cells by immunohistochemical and double immunofluorescence staining, the MSI status by immunоhistochemistry for 4 mismatch repair (MMR) proteins, and the genotype distributions for IL6 -174G/C (rs1800795) single-nucleotide polymorphism through PCR-RFLP method. Our results showed that serum IL-6 level were increased in CRC patients as compared with healthy controls (P<0.0001), and in patients with cancers with advanced histologic type (type IV). However, the higher concentration (above the median of 55.71 pg/mL) was with borderline association with longer survival of the patients after surgical therapy (P=0.055, Log rank test). We also found that IL-6+ immune cells prevailed in the invasive front (IF) of tumors compared with the tumor stroma (TS) (P<0.0001). More IL-6+ cells were recruited in the tumors with less advanced histologic type (I+II), with stronger inflammatory infiltrate in the IF, in early pTNM stages (I+II), without lymph node and distant metastases and the higher levels of IL-6+ cells, especially in the IF, were associated with longer survival (P=0.012). The results of our study suggest that although the serum levels of IL-6 are higher in CRC, the increased IL-6+ cells in tumor microenvironment, both in the invasive front and in tumor stroma, as well as the higher serum levels are associated with good prognostic variables and longer survival of the patients mainly in the early stages of CRC.

IL-6 Activities in the Tumour Microenvironment. Part 1.

The predominant role of IL-6 in cancer is its key promotion of tumour growth. IL-6 binds IL-6 receptor (IL-6R) and the membrane-bound glycoprotein gp130. The complex I-6/IL-6R/gp130 starts the Janus kinases (JAKs) and signal transducer and activator of transcription 3 (STAT3) or JAK/STAT3 pathway. IL-6 R exits in two forms: a membrane-bound IL-6Rα subunit (mIL-6R) that participates in classic signalling pathway and soluble IL-6R subunit (sIL-6R) engaged in trans-signalling. The pro-tumour functions of IL-6 are associated with STAT3, a major oncogenic transcription factor that triggers up-regulation of target genes responsible for tumour cell survival. IL-6 combined with TGF-ß induces proliferation of pathogenic Th17 cells. The anti-tumour function of IL-6 is the promotion of anti-tumour immunity. IL-6 trans-signaling contributed to transmigration of lymphocytes in high endothelial venules (HEV). Dendritic cell (DC) secreted IL-6 in the lymph node influences the activation, distribution and polarisation of the immune response. Elevated serum levels of IL-6 and increased expression of IL-6 in tumour tissue are negative prognostic marker for patients' survival.