Colon polyps and cytokines: emerging immunological mechanisms

Cell-mediated immune responses are an essential aspect of tumour-host interactions in colorectal cancers. The progression from precancerous (adenomatous) colon polyps to malignant colorectal cancer depends on a complex pathway involving the activities of activated T lymphocytes. The immune response is initiated when either cytotoxic T lymphocyte (CTL) CD8+ cells or CD4+ T-helper cells recognize the antigen from a human cancer cell. The cell-mediated response is largely initiated and controlled by the actions of various cytokines, which exert profound effects on T cell proliferation, cell-cell adhesion, apoptosis, and host immunity. The existence of an immune response to colon cancer is supported by studies of immunological treatments in humans and transplantable murine cancer models in animals. IL-2, IL-12, IFN-gamma, TNF-alpha, and TRAIL are implicated in enhancing cytotoxic and apoptotic effects in response to colon adenomas. In addition, growth factors, oncogenic cytokines and immunosuppressive factors may play a crucial role in the growth and survival of premaligant colonic tissue. This review aims to increase knowledge of the immunological mechanisms underlying colon tumour progression in the hopes that a greater understanding of the molecular pathways will lead to improved methods of prognosis and treatment.