T Cell (T Lymphocyte)- Definition, Types, Development, Applications


T cells are a type of white blood cell that is an essential part of the immune system . They are one of two primary types of lymphocytes, the other being B cells, that determine the specificity of immune response to antigens (foreign substances) in the body. T cells originate in the bone marrow and mature in the thymus . They play a central role in the adaptive immune response and can be distinguished from other lymphocytes by the presence of a T-cell receptor on their cell surface . T cells are important for cell-mediated immunity and the activation of immune cells to fight infection.

There are different types of T cells that perform different functions in the immune system. These include:

  • Helper T cells (CD4+ T cells): These are lymphocytes that assist the maturation of other lymphocytes like B cells to differentiate into plasma cells and memory B cells. They also secrete cytokines that regulate the overall immune response.
  • Cytotoxic T cells (CD8+ T cells): These are lymphocytes that destroy virus-infected cells or tumor cells as well as cells involved in transplants. They recognize their target cells by binding to short peptides present together with class I MHC molecules.
  • Memory T cells: These are long-lived lymphocytes that can quickly expand into a large number of effector T cells when re-exposed to the antigen that activated them in the first place. They provide long-term immunity against specific pathogens.
  • Regulatory T cells: These are lymphocytes that control immune reactions and prevent autoimmune diseases. They suppress autoreactive T cells that escape the negative selection process in the thymus.

The development and maturation of T cells involve a complex process of gene rearrangement, selection, activation and differentiation. The process begins with hematopoietic stem cells in the bone marrow that differentiate into common lymphoid progenitors. A subset of these progenitors migrates to the thymus, where they become engrafted and undergo further differentiation into various types of T cells. The thymus provides a specialized microenvironment that supports the development of T cells and ensures their self-tolerance and diversity .

T cells are crucial for the protection of the body against various pathogens and harmful cells. They can also be used for immunological treatments for cancer, such as chimeric antigen receptor (CAR) T cell therapy. This involves engineering T cells to express receptors that can recognize specific antigens on malignant cells and kill them.