Developmental markers of T lymphocytes

Developmental markers of T lymphocytes:
·        Developing thymocytes pass through a series of distinct stages which are marked by changes in the expression of T cell receptor, cell-surface proteins such as the CD3, CD4, and CD8.

·        These surface markers reflect the maturation of the cell, and particular combinations of cell-surface proteins are used as markers for T cells at various stages of differentiation.
·        The early cell that is committed to become a T cell in the thymus expresses only the CD3 marker. Because they do not express CD4 or CD8 they are called 'double-negative' thymocytes or immature T cells.
·        After which, CD4 and CD8 are expressed by the same cell; these are known as 'double positive' thymocytes. These cells enlarge, divide and express low levels of T cell receptor.
·        Those cells whose receptors can interact with self-peptide and self-MHC molecular complexes lose expression of either CD4 or CD8 and increase the level of expression of the T-cell receptor. The outcome of this process is the 'single-positive' thymocytes, which, after maturation, are exported from the thymus as mature single-positive CD4 or CD8 T cells.

Function of helper T cells and cytotoxic T cells
·        T cells are critical in regulation, activation, and action of the adaptive immune system.
·        They are “born” in the bone marrow but “mature” in the thymus.
·        Within the thymus both positive and negative selection occurs, resulting in specialized T cells with different clusters of differentiation (CD) on their cell surface; the main cell types are CD4+ and CD8+ T cells.

CD4+ T Cells:
These “helper T cells” undergo further differentiation after appropriate stimulation by interleukins to become either Th1 or Th2 cells with specific functions to help regulate both the humoral and cell-mediated immune system.

Th1 cells:
·        Th1 cells are involved in the regulation of the cell-mediated response.
·        They are activated by APCs and secrete interferon-Y (IFN-Y), which activates antigen presenting cells (APCs) for efficient killing.
·        They also secrete IL-2, which activates CD8+ (cytotoxic T cells) to kill virally infected cells.
·        Another cytokine secreted by Th1 cells is TNF- ß, which activates macrophages, inhibits B cells, and is directly cytotoxic for some cells.

Th2 cells:
·        These cells are mainly involved in activating B cells.
·        They enhance isotype switching by secreting IL-4, IL-5, and IL-6.
·        They activate eosinophils and mast cells too.
·        They also secrete IL-10, which inhibits the development of Th1 cells and cytokine release from macrophages.

Development of Th1 and Th2 cells from CD4+ T cells: How does the CD4+ T cell decide in which subtype to develop? The answer to this is cytokines!
·        Exposure to IL-4 and IL-5 (also IL-9 and IL-13) favors the development of Th2 cells.
·        IFN-Y and IL-12 (and its relatives IL-23 and IL-27) favor Th1 cell development.

CD8+ T Cells:
Also known as cytotoxic T cells, these cells are responsible for seeking out and eliminating virus/parasite-infected cells, cancer cells, and other foreign cells.
·        They induce apoptosis in target cells.
·        They also release the cytokines IFN-Y, TNF -A, and TNF-ß, which contribute to host defense.
It is important to understand the main steps involved when viral antigen is taken up by an APC to the point at which CD8+ T cells are “seeking and destroying” the infected cells.
·        When an APC (mainly dendritic cell or macrophage) is exposed to viral antigen, it will load the antigen onto an MHC II for presentation to a CD4+ T cell. It will also express a co-stimulatory signal on its cell membrane (e.g., B7). The TCR can then interact with the antigen-positive MHC II on the APC.
·        A single signal is not enough for activation. The immune system’s checks and balances require a second signal for appropriate activation to occur. The B7 co-stimulatory signal on the APC must interact with CD28 on the CD4+ T cell while the TCR–MHC II interaction is occurring.
·        If these conditions are met, the CD4+ T cell will release IFN-γ to stimulate the APC to efficiently kill its pathogen. The CD4+ T cell will also release IL-2 to (1) cause activation and proliferation of CD8+ cytotoxic T cells to kill virally infected host cells, and (2) cause CD4+ T cell proliferation and differentiation in an autocrine manner.

Self-reactivity: What happens when a TCR recognizes and binds to host antigens? In a healthy individual, the way the immune system tackles this issue is by anergy, deactivating that self-reactive T cell. If this process fails, it could potentially lead to the development of an autoimmune disease.

You can support Immunowesome by:
1. Donating via PayPal

2. Or buy supporting the authors website (by visiting and sharing the page!)
Visit by Bobby V. Shirke
Visit by Nakeya Dewaswala

1 comment:

  1. Will you become our next big winner? Win like, Laptop, Car, Cash, Or more. Enter in our free online sweepstakes, Free online Giveaways and Free Online contests, Don't Miss your Chance. Hurry! Sweepstakes-Online

    list of current sweepstakes,

    Millennium Rocket Giveaway,

    origin pc millennium giveaway,

    Origin PC Millennium Rocket,

    Origin PC Millennium Rocket Giveaway,

    Origin PC Millennium Rocket Giveaway 2020,