Immune system

• Immune System


  • Protects against infection and microbes
  • Isolates and removes nonmicrobial foreign substances
• Microorganisms


  • Virus
  • Bacterium
  • Parasites
  • Fungi
• Organization of the Immune System


  • Nonspecific immune response (innate)
  • Specific immune response (adaptive)
• Microorganisms are everywhere
• Culturing microorganisms


  1. Sterile cotton swab

  2. Culture dish with tryptic soy agar

  3. Culture dish after 4 days
• Nonspecific Immunity


  • Prevention
  • Attack
• Prevention to Infection


  • Physical barriers
  • Chemical barriers
  • Reflexes
• Physical Barriers


  • Mucous membrane of the digestive system
  • Mucous membrane of the respiratory system
  • Fibrous layer of the eyes
  • Skin
• Lysozyme


  Enzyme secreted from the mucous membranes
• Defensins


  Peptides secreted from the mucous membranes
• Sebum


  Oily acidic substance released from sebaceous glands
• Lymphoid Tissues


  • Bone marrow
  • Thymus
  • Adenoids
  • Tonsils
  • Lymph nodes
  • Spleen
  • Lymphatic vessels
• Immune Cell Production


  1. Hematopoietic stem cell

  2. Myeloid stem cell

  3. Lymphoid stem cell

  4. Reticulocyte

  5. Megakaryocyte

  6. Granulocyte/monocyte progenitor

  7. Erythrocyte

  8. Platelets

  9. Basophil

  10. Eosinophil

  11. Monocyte

  12. Neutrophil

  13. B-lymphocyte

  14. Natural killer cells

  15. T-lymphocyte

  16. Dendritic cell
• Phagocytic Cells


  • Neutrophils
  • Eosinophils
  • Macrophages
  • Dendritic cells
• Neutrophils


  • Most abundant phagocytic cells
  • Release cytokines, vasodilators and chemotaxins
• Monocytes/Macrophages


  • Engulf and digest
  • Activate T cells
  • Once monocytes enter tissue they become macrophages
• Mast Cells


  • Found throughout connective tissues (not found in blood)
  • Release histamine and other chemicals involved in inflammation
• Dendritic Cells


  • Phagocytic cells
  • Activate T cells
• Lymphocytes


  • Provide the immune system with diversity, specificity, memory, and the ability to distinguish between self and nonself
  • Three major types: B lymphocytes, T lymphocytes, Natural killer cells (null cells)

  
• B Lymphocytes


  • Transform into plasma cells and release antibodies into the circulation
  • Form memory cells
• Cytotoxic T Cell


  • Release perforin and granzymes (lysis)
  • Induce apoptosis (Fas)
• NK Cells


  • Important in fighting viral infections
  • They kill virus infected cells by a mechanism similar to cytotoxic cells
• Nonspecific immune response (innate) protects against foreign substances without having to recognize their identity
• Specific immune response (adaptive) is highly specific
• Nonspecific Immunity


  • Immune cells distinguish self from pathogens by identifying the pathogen-associated molecular patterns receptors (PAMPs)

  
• Parts of the Nonspecific Immunity


  • Barriers
  • Inflammation
  • Interferons
  • Natural killer cells
  • Complement system

  
• Skin Penetration


  1. Sharp object penetrating skin

  2. Microbes and foreign matter enter

  3. Macrophages detect and respond
• Inflammation


  1. Occurs through cut or injury to the skin

  2. Sequence of events to protect the body against infection
• Phagocytosis & Recruitment


  • Macrophages detect bacteria and engulf them
  • Macrophages release cytokines
  • Mast cells release histamine
  • Injured cells release chemotaxins
• Vasodilation & Increased Permeability


  • Histamine causes vasodilation, increasing blood flow and delivery of proteins
  • Proteins gain entry from blood to interstitial fluid

  
• Containment of foreign matter


  • Mast cells and basophils release heparin to prevent clot formation initially
  • Clotting factors form a clot in tissue, preventing spread of foreign matter
  • Scab forms
• Phagocytic Cell Migration


  1. Margination

  2. Diapedesis

  3. Chemotaxis
• Phagocytosis


  • Attachment
  • Internalization
  • Degradation
  • Exocytosis
• Cytokines


  • Attachment of macrophages to pathogen triggers their release
  • Act on the hypothalamus, liver, and immune cell proliferation and recruitment
• Interferons


  • Proteins secreted by leukocytes and virus-infected cells to induce virus resistance in neighboring cells
  • Interferons-gamma secreted from active T cells and NK cells, inhibit viral replication, enhance phagocytosis, boost antibody production, and activate NK cells and cytotoxic T cells

  
• Natural Killer Cells


  • Recognize abnormal or infected cells
  • Cause lysis of pathogen by secreting perforins
  • Can attack virus-infected cells without identifying virus
  • Actions enhanced by interleukin-2 and antibodies

  
• Complement system


  • Approximately 30 proteins participate in the response cascade, resulting in MAC reaching the surface of bacteria
  • Classical pathway, Lectin pathway, Alternative pathway
• Activation of Complement system


  1. Classical pathway: Binding to antibodies attached to bacteria

  2. Lectin pathway: Binding to mannose-containing carbohydrates on bacteria or viruses

  3. Alternative pathway: Binding to carbohydrates on bacterial cell walls
• Membrane Attack Complex (MAC)


  Embeds itself in the microbe membrane forming pores, allowing water and salt to enter and cause lysis
• Activation of Complement system Pathways


  1. Classical pathway

  2. Lectin pathway

  3. Alternative pathway