The Cellular Events Associated With Tumor Immunity

Body processes depend on careful regulation of cell division. A cell that is proliferating in an uncontrolled fashion will give rise to a growing clone of cells that eventually develops into a tumor or neoplasm. Malignant transformation is associated with complex genetic alterations. Tumor cells may differ antigenically from normal cell in that they gain or lose cell membrane molecules and they will be regarded as foreign and attacked by the cells of immune system. The involvement of the immune system in the host response to tumors is complex and involves both lymphocytes and lymphocyte-derived mediators, as well as inflammatory cells and various other agents such as complement. Both cell mediated and humoral immunity can have anti-tumor activity. Immune surveillance is the recognition and destruction of non-self tumors cells on their appearance by immune system. When Immune surveillance is imperfect then tumors escape from destruction. The strongest evidence for the existence of immuno-surveillance is increased frequency of cancers in immunedeficient hosts. These mechanisms may reflect pathologic derangements of normal immunoregulatory processes or may involve the production of suppressive substances by the tumors themselves. The major mechanism of tumor cell destruction involve attack by Natural Killer (NK) cells, cytotoxic T-cells, activated macrophages and antibodies. Tumor cells express normal levels of MHC class I antigens, thus they are destroyed by cytotoxic T-cells. NK cells have capacity to kill transformed cells in a non-specific fashion. T-cell and NK cells secrete a cytokine which activate the macrophages. Receptors on NK cells (NKG2D) recognize stress induced antigens and help in direct destruction of tumor cells.