Immune System Podcast Overview of the Immune System

Overview of the Immune System

• Discussion focuses on key components of the immune system:

  • Innate pathway

  • Cell-mediated pathway

  • Humoral-mediated pathway

  • Hypersensitivity reactions

First Line of Defense

• Skin and Mucosa

  • The skin serves as the first line of defense, composed of stratified squamous epithelium.

  • The skin includes layers of flattened, dead cells, which resist dehydration and pathogen entry.

  • The living cells rest on a basal lamina, a connective mesodermal barrier that restricts entry/exit of substances.

• Barriers by Ectoderm and Endoderm

  • Includes mucosal layers of respiratory and gastrointestinal tracts.

  • Exocrine components that assist the immune system:

  • Saliva: Secretes lysozymes and other substances to inhibit bacterial growth.

  • Tears and Conjunctiva: Alter pH and curtail the growth of specific bacteria.

• Microbiome

  • Non-sterile environments of skin and mucosa contain bacteria essential for immune function.

  • A balanced microbiome competes with pathogens, protecting skin and intestine.

Structures of the Immune System

• Epithelial Layers

  • Trachea and bronchioles: Lined with ciliated pseudostratified epithelial cells.

  • Cilia move trapped pathogens in mucus out of the lungs (e.g., swallowing, coughing).

• Gastrointestinal Canal

  • Upper and lower ends are lined with stratified squamous epithelium and secretory cells.

  • Stomach’s low pH denatures bacteria, serving as a significant barrier to infection.

  • Mucosal-associated lymphoid tissue (MALT) exists throughout the respiratory and GI tracts, facilitating local antibody production against pathogens.

  • Renal system lacks mucosal-associated tissue, relying on lymph nodes and phagocytes for defense.

Lymphatic and Immune Responses

• Lymphatic System

  • Contains numerous lymph nodes, strategically located in neck, axilla, and groin to filter pathogens and facilitate immune responses.

  • The Thymus:

  • Located near the heart, prominent in fetus and childhood, diminishes after age 25 due to memory immunity development.

  • Functions as a primary organ for immune cell maturation.

Blood Components and Immune Cells

• Centrifugation Analysis of Blood

  • Blood separates into plasma, buffy coat (white blood cells, platelets), and erythrocytes.

  • Leukocytes: Key immune cells with different functions:

  • Neutrophils: Major antigen-presenting cells; most abundant white blood cells.

  • B and T Lymphocytes: Specific immune response cells that require staining for identification.

  • Monocytes, Eosinophils, Basophils: Present in lesser quantities with distinct roles.

• Blood Plasma

  • Composed of 7% proteins primarily produced by the liver, serves as an osmotic buffer.

  • Serum: Plasma devoid of clotting proteins (e.g., prothrombin, fibrinogen).

Coagulation Pathways

• Coagulation Process

  • Coagulation occurs through intrinsic and extrinsic pathways that activate factor X, leading to thrombin formation.

  • The Intrinsic Pathway (contact activation) involves the activation of factors XII, XI, IX, and X.

  • The Extrinsic Pathway begins with factor VII and is typically initiated by damage exposure to tissue factor.

  • Activated factor X cleaves prothrombin to thrombin, converting fibrinogen to fibrin to form clots.

Inflammatory Response

• Vasodilation and Inflammatory Mediators

  • Injury causes the release of cytokines, initiating vasodilation and inflammation to coordinate healing and defense.

  • Symptoms: Warmth, redness, swelling, pain as part of a protective response.

  • Enhanced blood flow brings vital nutrients and immune cells to the injury site.

Immune System Activation

• Innate Immune Response

  • Activated quickly upon injury or infection independent of specific pathogens.

  • Initial increased blood flow pushes pathogens away while cytokines coordinate immune cell recruitment.

  • Specificities of the pathways:

  • Neutrophils and macrophages handle bacteria/environments directly.

  • T lymphocytes are trained post-initial exposure during lymphatic filtering.

• Antigen Presentation and Immune Activation

  • Antigen-presenting cells process pathogens and display antigens through Major Histocompatibility Complex (MHC) molecules (Class I and II).

  • MHC Class I presents viral antigens to CD8+ cytotoxic T cells.

  • MHC Class II presents bacterial antigens to CD4+ helper T cells, leading to specific immune responses.

B and T Cells Functions

• T Lymphocytes

  • CD4+ cells coordinate immune responses and recruit phagocytes.

  • CD8+ cytotoxic T cells destroy infected cells, mainly in viral infections.

  • Natural killer cells serve as unspecific cytotoxic agents.

• B Lymphocytes and Antibodies

  • Produce antibodies specific for pathogens.

  • Memory cells enable faster responses to future infections by the same pathogen.

Vaccination and Herd Immunity

• Immunization Process

  • Vaccines expose individuals to attenuated pathogens to stimulate primary immune responses effectively, reducing future infection severity.

  • Herd immunity protects communities by reducing disease spread; high vaccination rates diminish pathogen transmission.

Hypersensitivity Reactions

• Types of Hypersensitivities

  • Type I: Immediate allergic reactions mediated by IgE (e.g., pollen allergies).

  • Type II: Cytotoxic responses caused by mismatched blood transfusions.

  • Type III: Autoimmune diseases, involving IgG/IgM causing tissue damage (e.g., lupus).

  • Type IV: Delayed hypersensitivities mediated by sensitized T cells (e.g., poison ivy).

Conclusion

• Understanding immune pathways is crucial for diagnosing and treating diseases, mitigating infections, and preventing hypersensitivity reactions.

• Comprehensive awareness of immunological responses is necessary for successful clinical practice and patient education regarding vaccines and immune health.