theca cells

(noun)

A group of endocrine cells in the ovary made up of connective tissue surrounding the follicle. They provide androgen synthesis and signal transduction between granulosa cells and oocytes during development.

Related Terms

  • thecal
  • cumulus
  • estrogen
  • luteinizing hormone surge
  • progesterone

Examples of theca cells in the following topics:

  • Hormonal Regulation of the Female Reproductive Cycle

    • Follicle-stimulating hormone induces the proliferation of granulosa cells in the developing follicles and the expression of luteinizing hormone (LH) receptors on these cells.
    • Under the influence of FSH, granulosa cells begin estrogen secretion.
    • LH induces androgen synthesis by theca cells, stimulates proliferation and differentiation, and increases LH receptor expression on granulosa cells.
    • This also causes endometrial cells to produce receptors for progesterone, which helps prime the endometrium to the late proliferative phase and the luteal phase.
    • The surge also initiates luteinization of theca and granulosa cells.
  • Puberty

    • LH stimulates the Leydig cells of the testes to make testosterone and blood levels begin to rise.
    • For females, as the amplitude of LH pulses increases, the theca cells of the ovaries begin to produce testosterone and smaller amounts of progesterone.
    • Much of the testosterone moves into nearby cells called granulosa cells.
    • Smaller increases of FSH induce an increase in the aromatase activity of these granulosa cells, which converts most of the testosterone to estradiol for secretion into the circulation.
  • Specific T-Cell Roles

    • T helper cells assist the maturation of B cells and memory B cells while activating cytotoxic T cells and macrophages.
    • Differentiation into helper T cell subtypes occurs during clonal selection following T cell activation of naive T cells.
    • Cytotoxic T cells (TC cells, or CTLs) destroy virus-infected cells and tumor cells, and cause much of the damage in in transplant rejection and autoimmune diseases.
    • Memory T cells comprise two subtypes: central memory T cells (TCM cells) and effector memory T cells (TEM cells), which have different properties and release different cytokines.
    • Regulatory T cells (Treg cells), also known as suppressor T cells, are crucial for the maintenance of immunological tolerance.
  • Natural Killer Cells

    • The role of NK cells is similar to that of cytotoxic T cells in the adaptive immune response.
    • NK cells provide rapid responses to virus-infected cells and respond to tumor formation by destroying abnormal and infected cells.
    • NK cells use wo cytolytic granule-mediated apoptosis to destroy abnormal and infected cells.
    • Virus-infected cells destroyed by cell lysis release their replicated virus particles into the body, which infects other cells.
    • Cells that are osponized with antibodies are easier for NK cells to detect and destroy.
  • Lymphoid Cells

    • The three major types of lymphocyte are T cells, B cells, and natural killer cells.
    • If cancer cells evade NK cell detection for long enough, however, they can grow into tumors that are more resistant to NK cell activity.
    • T cells are involved in cell-mediated immunity whereas B cells are primarily responsible for humoral immunity.
    • There are two types of T cells involved in adaptive, cell-mediated immunity.
    • Following activation, B cells and T cells leave a lasting legacy of the antigens they have encountered in the form of memory cells.
  • Maturation of T Cells

    • T cells belong to a group of white blood cells known as lymphocytes and play a central role in the cell-mediated branch of the adaptive immune system.
    • They are distinguished from other lymphocytes, such as B cells and natural killer cells (NK cells), by the presence of a T cell receptor (TCR) on the cell surface.
    • T cells can be either helper T cells or cytoxic T cells based on whether they express CD4 (helper) or CD8 (cytotoxic) glycoprotein.
    • A T cell is then signaled by the thymus to become a CD4+ cell by reducing expression of its CD8 cell surface receptors.
    • The remaining cells exit the thymus as mature naive T cells.
  • Maturation of B Cells

    • B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response, which is governed by T cells) .
    • Once a B cell encounters its cognate antigen and receives an additional signal from a T helper cell, it can further differentiate into either plasma B cells or memory B cells.
    • B cells exist as clones.
    • A single B cell or a clone of cells with shared specificity, upon encountering its specific antigen, divides to produce many B cells.
    • B cells that encounter antigen for the first time are known as naive B cells.
  • Lymphocytes

    • Subtype 2 helper T cells present antigens to B cells.
    • Suppressor T cells (T-reg cells) retain some of their ability to bind to self-cells.
    • Then mature helper T cells bind their antigen to naive B cells through BCRs.
    • Plasma cell and long-lived B cells that are the main source of antibodies.
    • Memory B cells are dormant B cells with the same BCR as the B cell from which they differentiated.
  • Clonal Selection and B-Cell Differentiation

    • B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response, which is governed by T cells).
    • B cells that have not been exposed to antigen, also known as naïve B cells, can be activated in a T cell-dependent or independent manner.
    • T cell dependent activation is activation of B cells by type 2 helper T cells in the lymph nodes.
    • B cell differentiation is the process by which B cells change into different types, such as plasma cells and plasma blasts.
    • T cell-dependent B cell activation, showing a TH2-cell (left), B cell (right), and several interaction molecules.
  • Types of Adaptive Immunity

    • Cell mediated immunity is controlled by type 1 helper T cells (Th1) and cytotoxic T cells.
    • Helper T cells facilitate the immune response by guiding cytotoxic T cells to pathogens or pathogen-infected cells, which they will then destroy.
    • Then T-cell produced proteases enter the pathogen and induce an apoptosis response within the cell.
    • Helper T cells secrete cytokines  such as interferon-gamma, which can activate cytotoxic T cells and macrophages.
    • This diagram of adaptive immunity indicates the flow from antigen to APC, MHC2, CD4+, T helper cells, B cells, antibodies, macrophages, and killer T cells.
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