Lymphatic System

• Lymphatic System


  Immune system, defense mechanism for body defenses

  
• Innate Immunity (Non-specific Resistance)


  • Involves leukocytes (mainly granulocytes), and proteins such as defensins, complement, lysozyme, and interferons; cytokines and organic acids in specific regions lower the pH locally to either kill entering microorganisms directly or inhibit their growth
  • The immunity is not acquired by drugs, but through ourselves
• Hydrochloric acid (HCI)


  Gastric juice, very low pH
• Defensins


  Short cationic polypeptides produced by neutrophils and various epithelial cells that kill bacteria by disrupting 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


  Paracrine factors from leukocytes and virus-infected cells that signal NK (Natural Killer) cells to kill such cells and adjacent cells to resist viral infection
• Paracrine signals


  Signals that act locally between cells that are close together
• Adaptive Immunity (Specific Resistance)


  • Develops more slowly, based on antigen presentation to lymphocytes
• Antigens


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


  Immunoglobulins produced by plasma cells after a progenitor B cell is activated by a specific antigen
• Types of Antibodies


  • IgG, IgD
  • IgM, IgE
  • IgA
• Major Histocompatibility Complex (MHC) Class I Molecules


  Found on surfaces of all nucleated cells bear fragments of their constituent proteins
• MHC Class II Molecules


  Only antigen-presenting cells (APCs)
• Two Folds of Specific Resistance


  • Active Immunity
  • Passive Immunity
• Naturally acquired active immunity

  When we get sick the infective agent will gain entry to the body, act as stimulant for antibody formation because the organism acts as antigen. The immunity is lifelong.
• Naturally acquired active immunity


  • Measles, chicken pox, hepatitis A
• Artificially acquired active immunity


  When the antigen has been deliberately introduced like injecting vaccines, they act as antigen to stimulate antibody formation.
• Artificially acquired active immunity

  • MMR, OPV, BCG
• Naturally acquired passive immunity


  Exhibited by the transfer of antibodies from mother's placenta to the fetus and transfer of antibodies from breast milk to the baby.
• Artificially acquired passive immunity


  Injection of artificially prepared substance like immune serum of gamma globulin. These two are antibodies preparation.
• Artificially acquired passive immunity


  • Anti-tetanus antibodies, diphtheria antitoxin
• Primary Lymphoid Organs


  • Bone Marrow for B Lymphocytes
  • Thymus for T lymphocytes
• Secondary Lymphoid Organs


  • Lymph Nodes
  • MALT
  • Spleen
• Secondary Lymphoid Organs

  Where B and T cells are often activated, proliferate, and begin to function
• Contains a meshwork of reticulin produced by fibroblastic reticular cells
• Antigen bound to the immunoglobulin receptors on B cells (BCRs)


  Antigen bound to the immunoglobulin receptors on B cells (BCRs) is endocytosed, processed, and presented on MCH class II proteins to helper T cell. These then secrete IL-4 and other cytokines that stimulate gene recombination and clonal proliferation of these specific B cells. They differentiate as plasma cells producing antibodies against the antigen that was originally bound and processed
• B Cells


  • Produce antibodies for humoral immunity
• 1. B-cell Receptors (BCRs)

  Are IgM or IgD antibodies on the cell surface
• T Cells


  • Function in cell-mediated immunity
• Classes of T Cells

  • CD4+ T helper cells
  • CD8+ cytotoxic T cells
  • CD4+CD25+ regulatory T cells
  • yδ T Cells - TCR chains
• Humoral immune system


  Deals with antigens from pathogens that are freely circulating, or outside the infected cells
• Cellular immunity


  Occurs inside infected cells and is mediated by T lymphocytes

  
• Thymus


  • Bilobed organ in the mediastinum, most active and prominent before puberty and undergoes involution with less activity in the adult, primary organ where T Cells are produced, originates from endoderm
• Thymic Cortex


  • Squamous Cells (Blood-thymus barrier)
  • Stellate Epithelial Cells (Cytoreticulum)
  • Squamous Cortical Cells (Corticomedullary barrier)
• Thymic Medulla


  • Stellate Epithelial Cells (Cytoreticulum)
  • Secondary Layer
  • Hassall Corpuscles (Aggregates of TEC)
• MALT


  • Found in the mucosa of most tracts, but is concentrated in the palatine, lingual and pharyngeal tonsils, Peyer patches, and the appendix, free lymphoid nodules in connective tissue of mucosal lining together with free lymphocytes
• Palatine Tonsils


  • Posterior part of the soft palate, covered by stratified squamous epithelium (infiltrated by dendritic cells & lymphocytes), 10 - 20 epithelial invaginations/ crypts, separating the LT from subadjacent structures is a band of dense CT that acts as a capsule/ barrier against spreading tonsil infections
• Pharyngeal Tonsil


  • Posterior wall of the nasopharynx, covered by ciliated pseudostratified columnar epithelium
• Lingual Tonsils


  • Posterior surface of the tongue, covered by stratified squamous epithelium with crypts