T cells, also known as T lymphocytes, a type of white blood cell and one of the main components of the adaptive immune system. T-cells play an important role in hosting an immune response against pathogens and work like soldiers who search out and destroy the targeted invaders.
The immature T-cells migrate to thymus gland in the neck.
Here, they get mature and differentiate into various types of mature T-cells and become active in the immune system in response to a hormone called thymosin and other factors.
The T-cells that are potentially activated against the body’s own tissues are normally killed or changed during this maturational process.
Production of T-Cells
T-cell originate from haematopoietic stem cells (HSC) which are produced in the bone marrow.
These haematopoietic stem cells now split into two progenitor groups, called myeloid and lymphoid progenitor cells, the latter of which then differentiate into T and B cells.
These T cells then migrate via blood to the thymus gland, in the anterior mediastinum, to undergo the process of maturation. Now, these cells enter the cortex and proliferate, mature and pass onto the medulla of the thymus.
From the medulla, mature T cells enter the circulation. Now, these mature T cells are capable of responding to antigens in the periphery.
Types of T-Cells
There are four main types of T cells, including :
CD4+ Helper Cells
These helper cells assist in the maturation of B cells into the plasma cells and memory B cells. The cells also help activate cytotoxic T cells and macrophages.
CD8+ Cytotoxic Cells
These cells cause lysis of virus-infected and tumour cells. Cells are also involved in transplant rejection.
CD8+ cytotoxic cells recognize their targets by binding to antigen associated with MHC Class I molecules which are present on the surface of all nucleated cells.
Memory T Cells
They differentiate into effector cells (CD4+ and CD8+ cells) and memory T cells, once they come into contact with an antigen naive T cells.
They are long-lived and can quickly expand to large numbers of effector T cells upon re-exposure to the antigen.
Natural Killer T Cells
These cells bridge the adaptive immune system with the innate immune system.
Whilst most T cells function based on recognition of MHC (major histocompatibility complex) class molecules, natural killer T cells are able to recognise other antigen classes.
Once activated they are also able to perform the same functions as CD4+ and CD8+ cells.
These cells are distinct from natural killer cells.
Role of T-Cells
T-cells play an important role in protecting against intracellular pathogens such as protozoa, viruses and intracellular bacteria, and in immunity to extracellular pathogens by providing help for the antibody response.
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