T cells
Introduction
T cells, also known as T lymphocytes, are a type of white blood cell that play a crucial role in the immune response. They are one of the main components of the adaptive immune system, which provides the body with a tailored defense against specific pathogens. T cells are named after the thymus, an organ situated behind the sternum where they mature.
Types of T cells
There are several different types of T cells, each with a unique role in the immune response.
Helper T cells
Helper T cells (Th cells) are the most abundant type of T cell. They are responsible for coordinating the immune response by activating other immune cells, such as B cells and cytotoxic T cells.
Cytotoxic T cells
Cytotoxic T cells (Tc cells) are the primary effector cells of the adaptive immune system. They are capable of directly killing infected cells, as well as cancer cells.
Regulatory T cells
Regulatory T cells (Tregs) play a crucial role in maintaining immune homeostasis by suppressing excessive immune responses that could lead to autoimmunity or tissue damage.
Memory T cells
Memory T cells are a subset of T cells that provide long-lasting immunity by remembering specific pathogens. They can rapidly respond to subsequent encounters with the same pathogen, providing a faster and more effective immune response.
T cell development
T cells originate from hematopoietic stem cells in the bone marrow. These cells migrate to the thymus, where they undergo a complex process of maturation and selection.
Positive selection
Positive selection tests whether T cells can recognize and bind to self-MHC molecules. Only those T cells that can bind to MHC molecules with a certain affinity are allowed to survive.
Negative selection
Negative selection tests whether T cells react against self-antigens. T cells that bind too strongly to self-antigens are eliminated to prevent autoimmunity.
T cell activation
T cell activation occurs when a T cell receptor (TCR) recognizes and binds to a specific antigen presented by an MHC molecule on the surface of an antigen-presenting cell (APC). This triggers a series of intracellular signaling pathways that lead to T cell proliferation and differentiation.
Costimulation
Costimulation is a secondary signal required for full T cell activation. It involves the interaction between costimulatory molecules on the T cell and the APC.
T cell functions
T cells perform a variety of functions in the immune response, including:
- Direct killing of infected or cancerous cells (cytotoxic T cells)
- Activation of other immune cells (helper T cells)
- Suppression of immune responses (regulatory T cells)
- Memory of past infections (memory T cells)
T cells and disease
T cells are involved in a variety of diseases, including autoimmune diseases, infectious diseases, and cancer.
Autoimmune diseases
In autoimmune diseases, T cells mistakenly recognize self-antigens as foreign and mount an immune response against the body's own tissues. Examples include type 1 diabetes, rheumatoid arthritis, and multiple sclerosis.
Infectious diseases
In infectious diseases, T cells play a crucial role in controlling and eliminating the pathogen. However, some pathogens have evolved strategies to evade T cell responses.
Cancer
In cancer, T cells can recognize and kill cancer cells. However, cancer cells often develop mechanisms to evade T cell recognition or to inhibit T cell function.
T cell therapies
T cell therapies are a promising area of research in the treatment of cancer and other diseases. These therapies involve the manipulation of T cells to enhance their ability to recognize and kill disease cells.
CAR T-cell therapy
CAR T-cell therapy is a type of immunotherapy that involves genetically modifying a patient's own T cells to express a chimeric antigen receptor (CAR) that can recognize a specific antigen on cancer cells.