defense response to tumor cell

Definition

Target type: biologicalprocess

Reactions triggered in response to the presence of a tumor cell that act to protect the cell or organism. [GOC:add, ISBN:0781735149, PMID:16730260]

The defense response to tumor cells is a complex and multifaceted process that involves a variety of immune cells, signaling pathways, and effector mechanisms. It is triggered by the recognition of tumor-associated antigens (TAAs), which are molecules expressed by tumor cells that are different from those found in normal cells. These TAAs can be proteins, carbohydrates, or lipids.

The immune system's recognition of TAAs is mediated by specialized immune cells called antigen-presenting cells (APCs), such as dendritic cells and macrophages. APCs engulf tumor cells or their fragments and process the TAAs into smaller peptides. These peptides are then presented on the surface of the APC in association with major histocompatibility complex (MHC) molecules.

MHC molecules are proteins that display peptides to other immune cells, such as T lymphocytes (T cells). T cells are responsible for recognizing and destroying cells that display foreign antigens, including TAAs. There are two main types of T cells involved in the defense response to tumor cells:

* **Cytotoxic T lymphocytes (CTLs):** CTLs recognize and kill tumor cells directly. They do this by releasing cytotoxic granules that contain substances like perforin and granzyme, which can puncture the tumor cell membrane and induce apoptosis (programmed cell death).
* **Helper T lymphocytes (Th cells):** Th cells do not directly kill tumor cells but instead help to activate other immune cells, such as CTLs, macrophages, and B lymphocytes (B cells). Th cells produce cytokines, which are signaling molecules that can stimulate other immune cells to proliferate and differentiate into effector cells.

Macrophages are another important component of the defense response to tumor cells. They can directly kill tumor cells through phagocytosis (engulfing and destroying) or by releasing cytotoxic substances. Macrophages can also contribute to the activation of CTLs and Th cells.

B cells are responsible for producing antibodies, which are proteins that can bind to TAAs on the surface of tumor cells. Antibodies can neutralize tumor cells, making them more susceptible to attack by other immune cells, or they can trigger the complement pathway, which is a series of proteins that can lyse (destroy) tumor cells.

The defense response to tumor cells is often impaired in cancer patients, allowing tumors to grow and spread. This can be due to a variety of factors, including:

* **Tumor cell evasion of immune surveillance:** Tumor cells can evade the immune system by downregulating the expression of TAAs, suppressing the expression of MHC molecules, or releasing immunosuppressive molecules that inhibit the activity of immune cells.
* **Immune system exhaustion:** Chronic exposure to tumor antigens can lead to the exhaustion of immune cells, resulting in their inability to effectively respond to the tumor.
* **Immunosuppressive therapies:** Some cancer treatments, such as chemotherapy and radiation therapy, can suppress the immune system, making patients more susceptible to infection and reducing the effectiveness of the defense response to tumor cells.

Despite these challenges, the immune system remains a powerful tool for fighting cancer. Immunotherapy is a rapidly evolving field that aims to enhance the immune system's ability to recognize and destroy tumor cells. Immunotherapies include:

* **Cancer vaccines:** Vaccines that stimulate the immune system to produce antibodies or CTLs that target TAAs.
* **Immune checkpoint inhibitors:** Drugs that block the activity of molecules that inhibit the immune system, allowing it to attack tumor cells more effectively.
* **Adoptive T cell therapy:** Involves harvesting T cells from a patient's blood, modifying them to express receptors that recognize specific TAAs, and then infusing them back into the patient to attack the tumor.

Immunotherapies are showing promising results in clinical trials and are becoming increasingly important for treating a variety of cancers.'
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