The association between the immune system and malignancy : a brief review

Abstract

The immune system has evolved to protect the host from a universe of pathogenic microbes and eliminate toxic substances from the body. It is an interactive network of lymphoid organs, cells, humoral factors, and cytokines. The essential function of the immune system in host defence is best illustrated when it goes wrong: decreased activity results in severe infections and tumours of im- munodeficiency, and increased activity in allergic and autoimmune disease. Immune cells scan for the occurrence of any molecule that they consider to be foreign to the body, and transformed cells acquire antigenicity, which is recognised as non-self. A specific immune response is generated, and it results in the proliferation of antigen-specific lymphocytes. Immunity is acquired when antibodies and T-cell receptors are expressed and up-regulated through the formation and release of lymphokines, chemokines and cytokines. Both innate and acquired immune systems interact to initiate antigenic responses against carcinomas. There is an increas- ing body of recent evidence to support the role that the immune system plays in eliminating pre-clinical cancers. Tumour infiltration by immune cells has been shown to have powerful prognostic significance in a host of cancer types. Cytotoxic therapies, including Low Level Laser Therapy (LILI) and chemotherapy, induce potentially immunogenic cell death, releasing tumour-associated antigens in the context of a 'danger' signal to the immune system. An understanding of the interaction between immune cells, tumour cells and treatment modalities will therefore guide the future combination of immunotherapy with conventional therapy to achieve optimal anti-tumour effects.