Examples of theca cells in the following topics:
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.