IMMUNE SYSTEM AND LYMPHOID ORGANS

• Immune System


  It provides defense or immunity against infectious agents ranging from viruses to multicellular parasites
• Immune System


  It consists of a large, diverse population of leukocytes located within every tissue of the body and lymphoid organs interconnected only by the blood and lymphatic circulation
• Two fundamental lines of defense in our immune system:

  • Innate Immunity
  • Adaptive Immunity
• Innate Immunity


  It represents the first line of defense to an intruding pathogen
• Innate Immunity


  It is an antigen-independent (non-specific) defense mechanism that is used by the host immediately or within hours of encountering an antigen
• Innate Immunity


  It act as a physical barriers such as the skin and mucous membranes of the gastrointestinal, respiratory, and urogenital tracts that prevent infections or penetration of the host body
• Innate Immunity


  A line of defense that involves leukocytes (mainly granulocytes) and proteins
• 4 proteins of Innate Immunity

  • Defensins
  • Lysozyme
  • Complement
  • Interferons
• Defensins


  A protein that is a short cationic polypeptides produced by neutrophils and various epithelial cells that kill bacteria by DISTRUPTING the cell walls
• Lysozyme


  An enzyme made by neutrophils and cells of epithelial barriers, which HYDROLYZES bacterial cell wall components, killing those cells
• Complement


  A system of proteins in blood plasma, mucus, and macrophages that react with bacterial surface components to aid removal of bacteria
• Interferons


  A protein that is a paracrine factors from leukocytes and virus-infected cells that signal NK cells to kill such cells and adjacent cells to resist viral infection.
• Hydrochloric Acid


  Lower the pH locally to either kill entering microorganisms directly or inhibit their growth.
• Adaptive Immunity


  More specific, develops more slowly and is based on antigen presentation to lymphocytes which involves response by the B and T lymphocytes
• Adaptive Immunity


  Responses are aimed at SPECIFIC microbial invaders and involve production of memory lymphocytes so that a similar response can be mounted very rapidly if that invader ever appears again
• Adaptive Immunity


  Can be acquired gradually by being exposed to microorganisms
• Antigens


  Usually a proteins that are recognized by lymphocytes to elicit a specific immune response against them.
• Antibodies


  An immunoglobulins produced by plasma cells after a progenitor B cell is activated by a specific antigen
• Major Histocompatibility Complexes 


  Are cell surface glycoproteins whose primary function is to present peptide fragments for recognition by the appropriate T cells (lymphocytes)
• MCH Class I and II Molecules


  Both of them have the common task of presenting peptides to be recognized by T cells on the cell surface
• MCH Class I Molecules


  It is found on surfaces of all nucleated cells bear fragments of their constituent proteins of MHC
• MCH Class II Molecules


  Only antigen- presenting cells (APCs) of MHC
• Two forms of adaptive immune response:

  • Humoral Immunity

  • Cell-Mediated Immunity
• Humoral Immunity


  The B cell lymphocytes, a type of immune cell that makes antibodies after detecting a specific antigen, are principally responsible for this method
• Cell- mediated immunity


  Mature T cell lymphocytes, macrophages, and the production of cytokines in response to an antigen are its main drivers.
• Lymphocyte origin or differentiation can come from Primary or Secondary lymphoid organ
• Two primary lymphoid organs:

  • Bone marrow

  • Thymus
• Primary Lymphoid Organs


  Maturation of T cell and B cell
• Bone Marrow


  A primary lymphoid organ where cells destined to become B lymphocytes remain and differentiate further in the bone marrow
• Thymus


  A primary lymphoid organ which is the progenitors of T lymphocytes move via the circulation while being developed in this organ
• Secondary Lymphoid Organ


  This is where T cell and B cell become functional
• Secondary lymphoid organ


  These lymphoid organs are where lymphocytes are often activated, proliferate, and begin to function
• Secondary lymphoid organs


  These organs contain a meshwork of reticulin (where lymphocytes are being distributed) produced by fibroblastic reticular cells
• Thymus


  It originates from the endoderm and a bilobed organ in the mediastinum that is most active and prominent before puberty and undergoes involution with less activity in the adult.
• Thymus


  A primary lymphoid organ where T cells (T lymphocytes) are produced
• Mediastinum


  The midline of the thoracic cavity, that is surrounded by the left and right pleural sacs
• Two Divisions of the Thymus:

  • Thymic Cortex

  • Thymic Medulla
• Thymic cortex


  Has outer darkly basophilic and contains an extensive population of T lymphoblasts (thymocytes) located among numerous macrophages and associated with the unique TECs that have certain features of both epithelial and reticular cells
• 3 Thymic Epithelial Cells (TECs) in the Thymic Cortex:

  • Squamous Cells

  • Squamous Cortical Cells

  • Stellate Epithelial
• Squamous cell


  It forms a blood-thymus barrier preventing unregulated exposure of thymocytes to antigens