Host Response To Tumors

For immune response to foreign antigens include humoral mechanisms (eg., Antibodies) Cellular mechanisms Most humoral immune responses can not prevent tumor growth. Effector cells such as T cells, macrophages and natural killer cells, and had relatively effective ways to kill tumor cells. The activity of the effector cells is presented by cells, the tumor-specific antigens (TSA) or tumor associated antigens (TAA) on their cell surface (these cells are referred to as antigen presenting cells), and induced by cytokines (eg., Interleukins, interferons). Despite these effector cell immune response of the host can not prevent failure and therefore the occurrence and growth of a tumor. Cellular immunity for the direct detection and destruction of tumor cells, the T cells are primarily responsible. They exert an immunological monitoring function by proliferate after the detection of tumor-associated antigens and destroy the newly transformed tumor cells. The T-cell response against tumors is regulated by other cells of the immune system. Here, some T cells require the presence of humoral antibodies directed against tumor cells (antibody-dependent cellular cytotoxicity) to initiate the interactions that lead to the destruction of tumor cells. In contrast suppressor T cells inhibit the immune response to tumors. Cytotoxic T lymphocytes (CTL) recognize antigens on target cells and lyse them. These antigens may be cell surface proteins or intracellular proteins (e.g., as tumor-associated antigens) that are presented on the surface of cells in combination with MHC class I molecules. Tumor-specific cytotoxic T lymphocytes were found in neuroblastoma, malignant melanoma, sarcoma and colon, breast, cervical, endometrial, ovarian, testicular, nasopharyngeal and renal cell carcinoma. Another group of effector cells that destroy tumor cells, the natural killer cells (NK cells). Unlike the cytotoxic T lymphocytes NK cells the receptor for antigen recognition is lacking. Nevertheless, they can detect normal virus-infected cells and tumor cells. Your tumor cell-destroying activity is called “natural” because it is not induced by specific antigens. The underlying mechanism differ by the NK cells between normal and abnormal cells is currently under investigation. Initial results suggest that class I MHC molecules inhibit NK cells on the surface of normal cells and thus prevent their lysis. Thereby resulting the decreased expression of class I molecules, as is characteristic of many tumor cells, the activation of NK cells and subsequently lead to the tumor cell lysis. Macrophages destroy specific tumor cells when activated by a combination of factors. These include lymphokines (soluble factors produced by T cells) and interferon. However, they are less effective than the T-cell-mediated cytotoxic mechanisms. Macrophages can present tumor-associated antigens to T cells and thus stimulate tumor-specific immune response in certain circumstances. There are at least two classes of tumor-associated macrophages (TAM): TAM-1 (M1) – cells facilitate T-cell killing of tumors TAM-2 (M2) cells promote tumor tolerance Dendritic cells are antigen presenting cells, which occur in boundary tissues ( z., skin, lymph nodes). They play a central role in the initiation of tumor-specific immune response. These cells take tumor-associated proteins, process them and present tumor-associated antigens to T cells. In this way, they stimulate the response of cytotoxic T lymphocytes against the tumor. Several classes of dendritic cells can mediate tumor promotion or suppression. The lymphokines produced by immune cells stimulate the growth or induce the activity of other immune cells. These lymphokines include interleukin 2 (also known as T-cell growth factor) and interferons. IL-12 is produced by dendritic cells and induces specific cytotoxic T-lymphocytes, whereby an anti-tumor immune response is enhanced. Regulatory T cells are normally present in the body and help protect against autoimmune reactions. They are produced to pathogens during the active phase of an immune response and limit the strength of the immune response that might otherwise harm the body. An accumulation of these cells in tumors inhibits the immune response against the tumor. Myeloid suppressor cells consist of immature myeloid cells and their progenitors. These cells accumulate in large numbers in tumor diseases and effectively suppress immune responses. Humoral immunity In contrast to cytotoxic T-cell immunity seem to tumor growth to offer no significant protection humoral antibodies. Most antibodies can not recognize tumor-associated antigens. Nevertheless, in the serum of patients with various cancers (eg. As Burkitt’s lymphoma, malignant melanoma, osteosarcoma, neuroblastoma, lung carcinoma, breast carcinoma, and gastrointestinal carcinoma) were humoral antibodies that react in vitro with tumor cells, are detected. Cytotoxic antibodies directed against antigens on the surface of tumor cells. These antibodies can induce an anti-tumor effect on complement or serve as a marker for the destruction of tumor cells by T-cells (antibody-dependent cell-mediated cytotoxicity). Another group of humoral antibodies, the reinforcing antibody so-called (blocking antibodies), promote the growth of tumors rather than to inhibit it. The mechanisms and the importance of such immunological reinforcements but so far still not understood well. Failure of the host defense Although many tumors destroyed by the immune system and thus can never be discovered, while others continue to grow despite the presence of tumor-associated antigens. There are discussed various mechanisms to explain the inadequate host response against tumor-associated antigens such. B .: Specific immune tolerance to tumor-associated antigens in a process involved in the antigen presenting cells and suppressor T-cells may be secondary to prenatal exposure to this antigen Suppression of the immune response (by chemical, physical or viral influences z. B., T- helper cell destruction by HIV) suppression of immune response by cytotoxic drugs or radiation suppression of immune response by the tumor itself through various complex and largely misunderstood mechanisms leading to reduced function of T, B and antigen presenting cells, decreased IL-2 production and increased circulation of the soluble IL-2 receptor (by binding to IL-2 of this inactivated) leads. Presence and activity of TAM-2 (M2) – cells that promote tumor tolerance

Health Life Media Team

Leave a Reply