T lymphocytes
T lymphocytes, also known as T cells, are specialized white blood cells that play a crucial role in the immune system. Produced in the bone marrow, they mature in the thymus gland before entering the bloodstream to act as mediators of cellular immunity. T lymphocytes are essential for responding to various pathogens, foreign cells, and even tumor cells that may threaten the body. There are different types of T cells, including helper T cells (CD4+), which activate other immune cells through the secretion of signaling molecules, and killer T cells (CD8+), which directly attack infected or cancerous cells.
Additionally, regulatory T cells help prevent the immune system from mistakenly attacking the body’s own tissues, which is important in managing autoimmune conditions. The immune response involves a complex interaction of various cells, including antigen-presenting cells that help T lymphocytes recognize and respond to specific antigens. This intricate system allows the body to mount both general and targeted defenses against a wide range of threats, making T lymphocytes vital components of the adaptive immune system. Their ability to remember specific invaders enhances the immune response, ensuring more effective protection against future infections.
Subject Terms
T lymphocytes
- ALSO KNOWN AS: Helper T cells, killer T cells
Definition: specialized white blood cells that are essential components of the immune system
T lymphocytes are specialized white blood cells that are essential components of the immune system. Although produced in bone marrow, T lymphocytes migrate to the thymus gland to mature until they are needed. Normal lymphocytes and other types of white blood cells are always present in sufficient numbers to fight infection, but special T lymphocytes are released into the bloodstream by the immune system to perform as mediators of cellular immunity. As such, they help humans respond at the cellular level to different types of disease-causing organisms (pathogens), foreign cells (non-self-cells) that have entered the body, tumor cells, and abnormal self-cells that attack the body’s own tissues.
Cell Activation and Function
T lymphocytes participate in hypersensitivity reactions, reactions to allergens or toxic substances, graft-versus-host reactionsas in transplantationand other types of immune reactions. The immune system activates what are called helper T cells (CD4+ T cells) when it detects specific types of proteins (antigens) on the surface of non-self-cells that have invaded the body. Helper T cells secrete cytokines and lymphokines (interleukins) that signal other white cells to increase their numbers and reinforce their normal functions.
Killer T cells (CD8+ cells) are activated to attack specific tumor cells and certain viruses and parasites whose surface antigens they recognize. Regulatory T cells perform a slightly different function, protecting against self-cells that mistakenly attack certain body tissues (such as joint tissue in rheumatoid arthritis or eye tissue in thyroid eye disease) in autoimmune disease.
Role in Disease
The role of the immune system in protecting the body relies on layers of defense provided by different activities of the innate immune system and the adaptive immune system. Consequently, the immune response can range from general, everyday protection against invaders by a relatively nonspecific response of the innate immune system to increasingly specific responses of the adaptive immune system, whose immunologic memory allows it to recognize certain invaders. Infectious organisms, foreign cells, and tumor cells all have unique protein-based antigens on their cell surfaces that can be detected by the adaptive immune system. These antigen-presenting cells (APCs) are targeted by immune system cells, which then bind to the antigens. This process, in turn, activates other immune system components, such as macrophages, growth factors, and natural killer cells, forming an integrated defense mechanism.
As a critical component of the adaptive immune system, T lymphocytes make up the body’s special reserve forces. They are called on when antigen-specific action is needed to halt the harmful activity of bacteria, viruses, parasites, tumor cells, cells from foreign tissue, or out-of-control self-cells that may be responsible for progressive disease.
Bibliography
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