Lecture 30 - Immunology and the Immune System

• Immunology


  The study of an organism's defense system (immune system) in health and disease
• Immune system


  An organised system of organs, cells and molecules that interact together to defend the body against disease (eg pathogenic microorganisms and cancer)
• Components of the immune system


  • Organs (eg. spleen)
  • Cells (eg. T cells)
  • Molecules (eg. antibodies, y shaped organism)
• Defensins


  • Small, cationic peptides that play a significant role in the innate immune response against microbial infections
  • Produced by various cells, including epithelial cells and immune cells such as neutrophils and macrophages
  • Exert antimicrobial activity by disrupting microbial cell membranes, leading to cell lysis and death
  • Effective against a wide range of pathogens, including bacteria, fungi, and viruses
  • Can modulate inflammation and contribute to wound healing
• Diseases affected by the immune response

  • Infectious diseases: HIV/AIDS, Tuberculosis, Influenza, Malaria, SARS-CoV-2
  • Inflammatory diseases
  • Autoimmune diseases: Arthritis/Rheumatism, Allergy/Asthma, Lupus, Diabetes, Crohn's Disease/ Inflammatory Bowel Disease, Multiple sclerosis
  • Cancer
• Microbes


  • Viruses - Tiny, require an electronmicrosope to be seen, an example is polio
  • Bacteria - Various shapes, can be in chains, single, have flagella etc.
  • Fungi
  • Protozoa, eg. Malaria
• Pathogenic microbes


  Disease causing microbes, what the immune response protects us against
• Primary lymphoid organs


  • Bone Marrow
  • Thymus
• Secondary lymphoid organs


  • Lymph Nodes
  • Spleen
• Primary lymphoid organs


  • Production of white blood cells (lymphocytes)
• Secondary lymphoid organs


  • Sites where immune responses are initiated
• Physical barrier: The skin


  • Epidermis - Dead cells, keratin and phagocytic immune cells
  • Dermis - Thick layer of connective tissue, collagen and blood vessels and phagocytic immune cells
  • Dendritic cells - A special type of immune cell that is found in tissues, such as the skin, and boosts immune responses by showing antigens on its surface to other cells of the immune system
• Chemical defenses of the skin

  • Antimicrobial peptides e.g. skin 'defensins' forms pores in microbial cell membranes
  • Lysozyme - Enzyme that breaks down bacterial cell walls
  • Sebum - low pH, from sebaceous glands, inhibitory to microbial growth as is acidic
  • Salt: hypertonic
• Mucous Membranes


  • Epithelium - Tightly packed live cells that are constantly renewed, mucus-producing goblet cells
  • Mucus layer - Mucus is produced by mucus-producing goblet cells
• Chemical defenses of mucosal surfaces


  • Stomach - Low pH
  • Gall bladder - Antimicrobial bile
  • Intestine - Digestive enzymes, damaging to invading microorganisms
  • Mucus - Traps microorganisms, can contain defensins
  • Lysozyme (Tears, urine) Enzyme that can break down bacterial cell walls
• Injuries can let invading organisms in


  Through tightly packed skin layers
• Innate immunity


  Already in place, Rapid (hours), Fixed, Limited specificities, Has no specific memory
• Adaptive immunity


  Improves during the response, Slow (days - weeks), Variable, Highly specific, Has long-term specific memory
• Innate immune system


  • Rapidly responds to pathogens, though it lacks specificity and memory
• Adaptive immune system


  • Improves its response over time, with specificity and memory for encountered pathogens
• Components of adaptive immune system


  • T cells
  • B cells
• T cells


  Mediate cellular immunity
• B cells


  Mediate humoral immunity
• Adaptive immune system is responsible for long-term protection, such as that provided by vaccines
• Primary function of immune system


  Protection of the body against threats from invading pathogens via processes such as phagocytosis and destruction via pathogenic lysosomes
• How immune system distinguishes self and non-self


  Via highly trained T cells, engineered from bone-marrow and trained in the Thymus to recognise themselves and invading foreigners
• Cell wall recognition of pathogens

  Cell walls have specific proteins that recognise building blocks common in particular species, sending signals to increase gene transcription and produce response proteins
• Diseases impacted by immune response


  • Infectious disease (e.g. influenza, polio, tuberculosis)
  • Inflammatory diseases (e.g. arthritis)
  • Cancer
  • Conditions like diabetes (when immune system attacks itself)
• Primary lymphoid organs and their functions


  • Bone marrow - producer of lymphocytes (white blood cells), including T cells
  • Thymus - trains T cells to recognise self and non-self
• Role of secondary lymphoid organs


  Sites where immune responses are initiated and coordinated
• How lymphatic vessels contribute to immune surveillance


  Transport lymphatic fluid containing white blood cells, antigens, and other immune components throughout the body, facilitating movement of immune cells and antigens to lymphoid organs
• Physical barriers of immune system


  • Epithelial tissue (skin)
  • Mucosal surfaces
• Structure and function of epithelial tissue


  Provides physical barrier, comprised of epidermis (dead cells, keratin, phagocytes) and dermis (connective tissue, blood vessels, phagocytes); chemical defenses include acidic pH, high salt content, lysozyme enzyme
• Structure and function of mucosal surfaces


  Line openings in body, comprised of live epithelium with mucus-producing goblet cells and a mucus layer; chemical defenses include mucus trapping pathogens, low pH, enzymes, antimicrobial compounds
• How mucous membranes contribute to pathogen defense


  Mucus traps and flushes out pathogens, contains antimicrobial compounds
• Examples of chemical defenses


  • Acidic pH of skin and stomach
  • Enzymes in urine, intestines, and gall bladder
  • Salt in tear ducts
• Difference between innate and adaptive immunity


  Innate is faster acting but less specific, adaptive has long-term memory and specificity
• How innate immunity provides rapid defense


  Broad, non-specific immune response works across most pathogens
• Role of T cells and B cells in adaptive immunity

  T cells work with adaptive system to form targeted responses, B cells mediate humoral immunity