granule cells

Examples of granule cells in the following topics:

• Cell Inclusions and Storage Granules

  • Sulfur is most often stored as elemental (S0) granules which can be deposited either intra- or extracellularly.
  • Sulfur granules are especially common in bacteria that use hydrogen sulfide as an electron source.
  • The internal microenvironment of a prokaryotic cell (pH, osmolarity) may differ from that of the original source of the gene.
  • In addition, the fine controls that may keep the concentration of a protein low will also be missing in a prokaryotic cell, and overexpression can result in filling a cell with ectopic protein that, even if it were properly folded, would precipitate by saturating its environment.
  • Explain the hypothesis regarding the formation of inclusion bodies and the importance of storage granules

• Development of the Dual Lymphocyte System

  • B cells and T cells are the major types of lymphocytes.
  • Mammalian stem cells differentiate into several kinds of blood cell within the bone marrow.
  • B cells mature into B lymphocytes in the bone marrow, while T cells migrate to, and mature in, a distinct organ called the thymus.
  • Effector lymphocytes function to eliminate the antigen, either by releasing antibodies (in the case of B cells), cytotoxic granules (cytotoxic T cells) or by signaling to other cells of the immune system (helper T cells).
  • Mammalian stem cells differentiate into several kinds of blood cell within the bone marrow.

• Natural Killer Cells

  • Natural killer cells (NK cells) are cytotoxic lymphocyte critical to the innate immune system.
  • NK cells provide rapid responses to virally infected cells and respond to tumor formation by destroying abnormal and infected cells.
  • NK cells use two cytolytic granule mediated apoptosis to destroy abnormal and infected cells.
  • The granules of NK cells contain proteins such as perforin and proteases known as granzymes.
  • Antibodies that bind to antigens can be recognized by FcϒRIII (CD16) receptors (a type of activating receptor), resulting in NK activation, release of cytolytic granules, and consequent cell apoptosis.

• Types of WBCs

  • A major distinguishing feature is the presence of granules; white blood cells are often characterized as granulocytes or agranulocytes.
  • These granules are membrane-bound enzymes that act primarily in the digestion of endocytosed particles.
  • They may also cause granule dependent cell-mediated apoptosis through the release of perforins, granzymes, and proteases.
  • The cells include:
  • Monocytes and their progeny contain toll-like receptors and granules.

• Natural Killer Cells

  • After a pathogen enters the body, infected cells are identified and destroyed by natural killer (NK) cells, which are a type of lymphocyte that can kill cells infected with viruses or tumor cells (abnormal cells that uncontrollably divide and invade other tissue).
  • As such, NK cells offer a complementary check for unhealthy cells, relative to T cells.
  • NK cells are always active; an interaction with normal, intact MHC I molecules on a healthy cell disables the killing sequence, causing the NK cell to move on.
  • After the NK cell detects an infected or tumor cell, its cytoplasm secretes granules comprised of perforin: a destructive protein that creates a pore in the target cell.
  • Phagocytic cells then digest the cell debris left behind.

• Lymphoid Cells

  • The three major types of lymphocyte are T cells, B cells, and natural killer cells.
  • Therefore it acts as an inhibitor of NK cell activity, and NK cells will activate and destroy cells when it does not detect MHC class I on that cell surface.
  • Activated NK cells release cytotoxic (cell-killing) granules that contain perforin and granzyme, which can lyse cell membranes and induce apoptosis to kill infected or abnormal cells.
  • 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.

• Phagocytes

  • Oxidative stress can kill a cell through DNA, cell membrane, or mitochondrial damage.
  • Mature monocytes have large, smooth, lobed nuclei and an abundant cytoplasm that contains granules, but are not technically considered granulocytes.
  • Macrophages do not have granules, but contain many lysosomes.
  • They also degranulate their granules to release perforin, granzyme, proteases, and other chemicals to do cytotoxic damage to pathogens (and occasionally normal bodily tissues as well).
  • In addition to these functions, mast cells produce cytokines kept in their granules, such as histamine that induce an inflammatory response when a pathogen is detected.

• Types of Adaptive Immunity

  • Cell mediated immunity is controlled by type 1 helper T-cells (Th1) and cytotoxic T-cells.
  • These cells are activated by antigen presenting cells, which causes the cells to rapidly mature into forms that are specific to that antigen.
  • Helper-T cells facilitate the immune response by guiding cytotoxic T-cells to pathogens or pathogen-infected cells, while the cytotoxic T-cells will kill the pathogens or pathogen-infected cells.
  • Some of the ways in which cytotoxic T-cells kill pathogens include the release of granules that contain the cytotoxins perforin and granzyme, which lyse small pores in the membrane of a pathogen.
  • Then T-cell produced proteases can enter the pathogen and induce an apotosis response within the cell.

• White Blood Cells

  • The role of white blood cells is very different from that of red blood cells.
  • One of the two main groups are the granulocytes, which contain granules in their cytoplasm, and include the neutrophils, eosinophils, and basophils ( a).
  • The second main group is the agranulocytes, which lack granules in their cytoplasm, and include the monocytes and lymphocytes ( b).
  • They include B cells, T cells, and natural killer cells.
  • T cells attack viruses, fungi, some bacteria, transplanted cells, and cancer cells.

• WBC Function

  • This process is performed primarily by mast cells, eosinophils, basophils, and NK cells.
  • When pathogens are encountered, granule dependent apoptosis (a mechanism of cytotoxicity) may be induced in the pathogen by releasing perforins, granzymes, and proteaseases from their granules.
  • Cell mediated activities.
  • This process is performed by T cells.
  • Memory cell activity.