Immunosuppressive Factors in Human Cancer

Abstract

This chapter reviews the factors on immunosuppressive molecules that are elaborated by tumor cells or found in sera and effusions. Immunosuppressive factors can be found in normal sera, but their level is increased in cancer sera. These factors may contribute to the defective cellular responses of patients. Some well-characterized immunosuppressive molecules are transforming growth factor β (TGF-β), lymphocyte blastogenesis inhibitory factor (LBIF), p15E, and suppressive E-receptor (SER). TGF-β is produced by most cells and has an extraordinarily wide range of biological activities. p15E protein possesses a remarkable range of immunosuppressive activities. The SER is isolated from malignant effusions derived from patients with several types of cancer and inhibited several cellular immune responses. The exact mechanism of the immunosuppression is still uncertain, but a multiplicity of factors contributes to its occurrence: suppressor T cells and suppressor macrophages, immune complexes, acute phase proteins, tumor-derived suppressor molecules, suppressor substances in sera and effusion fluids of patients, and chemotherapy and irradiation. The colony-stimulating factors, acute-phase proteins, and miscellaneous molecules are some of the immunosuppressive factors in human cancer.