LYMPHATIC SYSTEM

Cards (63)

  • The immune system provides defense or immunity against infectious agents ranging from viruses to multicellular parasites
  • Innate immunity

    Immediate and non-specific
  • Chemicals forming a major part of innate immunity
    • Hydrochloric acid (HCl) and organic acids
    • Defensins
    • Lysozyme
    • Complement
    • Interferons
  • Cytokines are used by cells in the immune system to communicate with each other during infection or inflammation
  • Antibodies
    Glycoproteins of the immunoglobulin family that interact specifically with antigenic determinants, secreted by plasma cells, each antibody combines with the epitope it recognizes
  • Antigens
    Molecules recognized by cells of the adaptive immune system, elicits immune response, immune cells react to small molecular domains known as antigenic determinants or epitopes
  • Medical terminologies: Epitope - antigenic determinant site, Paratope - antigen-binding site, Immunogens - molecule capable of eliciting an immune response, Haptens - non-immunogenic materials that can stimulate immune response when complexed with larger molecules, Adjuvant - substance administered with an immunogen to enhance the immune response
  • Types of immunity
    • Innate immunity
    • Adaptive immunity
  • Functions of cytokines
    1. Directed cell movements (chemotaxis)
    2. Increased mitotic activity in certain leukocytes
    3. Stimulation or suppression of lymphocyte activities in adaptive immunity
    4. Stimulated phagocytosis
  • Antibody classes
    • Immunoglobulin G (IgG) - most abundant class in blood, highly soluble and stable, crosses placental barrier, confers passive immunity to newborns
    • Immunoglobulin A (IgA) - present in exocrine secretions, relatively resistant to proteolysis, reacts with microorganisms in various secretions
    • Immunoglobulin M (IgM) - constitutes 5% of antibodies
  • Innate immunity
    • Physical barrier of skin
    • Mucous membranes
    • Toll-like receptors (TLRs)
    • Natural killer (NK) cells
    • Leukocytes and specific cells of the tissue barriers
  • Adaptive immunity
    Aimed at specific microbial invaders, mediated by lymphocytes and antigen presenting cells (APCs), acquired gradually by exposure to microorganisms, more specific, and slower to respond
  • Immunoglobulin M (IgM) constitutes 5%-10% of blood immunoglobulin and usually exists in a pentameric form united by a J chain
  • Immunoglobulin M (IgM) bound to antigen is the most effective antibody class in activating the complement system
  • Antigen-Presenting Cells
    • Macrophages
    • Lymphoid Dendritic Cells
    • Thymic Epithelial Cells
  • Immunoglobulin D (IgD)
    • The least abundant immunoglobulin in plasma, acts as an antigen receptor on B lymphocytes
  • Cytotoxic T cells (CTLs)

    • Recognize specific antigens on foreign or virus-infected cells and eliminate them by releasing perforins and granzymes causing apoptosis
  • Cells destined to become B lymphocytes
    Remain and differentiate further in the bone marrow
  • B and T cells
    Circulate to the peripheral secondary lymphoid organs after maturation in primary structures
  • Types of T lymphocytes
    • Helper T cells: CD4+
    • Cytotoxic T cells (CTLs): CD8+
    • Regulatory T cells (Treg, suppressor T cells)
    • γδ T cells
  • Immunoglobulin E (IgE)

    • Usually a monomer, triggers the liberation of biologically active substances in response to antigens, characterizing allergic reactions
  • J chain
    • Polypeptide uniting immunoglobulin M (IgM) in a pentameric form
  • Immunoglobulin M (IgM) is mainly produced in an initial response to an antigen
  • Lymphocytes
    • B lymphocytes
    • T lymphocytes
  • Progenitors of T lymphocytes
    Move via the circulation into the developing thymus
  • T cells recognize antigenic epitopes via surface protein complexes termed T-cell receptors (TCRs)

    T lymphocytes are said to be MHC restricted
  • Functions of antibodies
    • Complement activation
    • Opsonization
    • NK cells activation
  • Helper T cells
    • Characterized by CD4, help the immune system by making cytokines to activate various immune responses
  • γδ T CELLS
    • Smaller subpopulation with TCRs containing γ (gamma) and δ (delta) chains instead of α and β chains
    • Migrate to the epidermis and mucosal epithelia, becoming largely intraepithelial, and do not recirculate to secondary lymphoid organs
  • XIC T CELLS (CTLs)
    • They have T-cell receptors (TCRs) and CD8 coreceptors that attach to specific antigens on foreign or virus-infected cells shown by MHC class I molecules
    • They eliminate cells displaying antigens by releasing perforins and granzymes, causing apoptosis
    • Also known as Killer T cells
    • Activator: Interleukin-2 (IL-2)
  • T CELLS are developed in the THYMUS
  • LYMPHOID SYSTEM is composed of lymphocytes, lymphoid organs, and lymphatic vessels
  • Lymphoid tissues are usually reticular connective tissue filled with large numbers of lymphocytes
  • FUNCTIONS OF LYMPHOID ORGANS: Provide sites for lymphocytes to come into contact with antigens, promote proliferation and maturation of lymphocytes, promote B lymphocytes to become plasma cells producing antibodies
  • REGULATORY T CELLS (Treg, SUPPRESSOR T CELLS)
    • CD4+ CD25+ cells that inhibit specific immune responses
    • Produce peripheral tolerance supplementing central tolerance developed in the thymus
  • B LYMPHOCYTES
    • Surface receptors for antigens are monomers of IgM or IgD
    • Helper T cell activation triggers recombination in immunoglobulin genes and stimulates cell proliferation
    • Differentiate into plasma cells secreting antibodies that bind the same epitope recognized by the activated B cell
    • Some B cells remain as long-lived memory B cells
  • Specific surface proteins, known as “Cluster of Differentiation" (CD) markers, help distinguish between B cells and different subsets of T cells using immunocytochemical techniques
  • Primary Lymphoid Organs are also known as Central Lymphoid Organs
  • B CELLS are developed in the BONE MARROW
  • LYMPHOID ORGANS
    • Bone marrow
    • Lymph nodes
    • Thymus
    • Spleen
    • Mucosa-associated lymphatic tissue (MALT)