What are T lymphocytes? |

Definition

T lymphocytes are specialized white blood cells that are essential components of the immune system. Although they are 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 reactions (as in
transplantation), and 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

Chatilla, Talal A. “Role of Regulatory T Cells in Human Diseases.” Journal of Allergy and Clinical Immunology 116 (2005): 949–959.

Martin, Stefan F. T Lymphocytes as Tools in Diagnostics and Immunotoxicology. Basel: Springer, 2014. Digital file.

Monroe, John G., and Michael J. Lenardo. “Regulation of Activation of B and T Lymphocytes.” In Hematology: Basic Principles and Practice, edited by Ronald Hoffman et al. 6th ed. Philadelphia: Churchill Livingstone/Elsevier, 2009.

Sompayrac, Lauren M. How the Immune System Works. 5th ed. Ames, Ia.: Wiley-Blackwell, 2016.

“T-Cell Mediated Immunity.” In Janeway’s Immunobiology, by Kenneth Murphy, Paul Travers, and Mark Walport. 8th ed. New York: Garland Science, 2014.