Basic Immunology Lecture 1. The innate immune system.pptx

Basic Immunology How the body protects itself from infection Janis Shute Infection with what? Bacteria (E.coli; 7 μm long and 1.8 μm diameter) Virus (20-300 nm) Parasites Ascaris;15 to 35 cm Tapeworm; 30 m!! A bacterial population can double every 20 minutes – the race is on for the immune system to...

Basic Immunology How the body protects itself from infection Janis Shute Infection with what? Bacteria (E.coli; 7 μm long and 1.8 μm diameter) Virus (20-300 nm) Parasites Ascaris;15 to 35 cm Tapeworm; 30 m!! A bacterial population can double every 20 minutes – the race is on for the immune system to prevent infection The Immune System Innate immunity immunity Adaptive natural immune response acquired response - prevents or limits infection infection - non-specific - eradicates - highly specific The Innate Immune SystemPhysical, chemical and cellular barriers to all infection External defences- The skin Layers of closely packed keratinocytes Antimicrobial fatty acids in sebum from sebaceous glands Extracellular antimicrobial lipids; ceramide & sphingosine Acid pH of sweat (lactic acid) Antimicrobial peptides eg dermicidin in sweat from eccrine glands Mucus membranes in the respiratory tract & gut Epithelial tight junctions prevent infection Mucus is produced by goblet cells in the epithelium and by mucus glands in the lower respiratory tract Cilia in the lower respiratory tract move the mucus up toward the larynx. Epithelial cells produce antimicrobial peptides (defensins) and lysozyme Goblet cell Symbiotic bacteria in gutcompete with pathogens for nutrients and sites of attachment Other external innate immune defences; The flow of tears, urine, saliva, perspiration, vaginal secretions, to prevent microbe adhesion to epithelial surfaces Lysozyme (muramidase) in tears, saliva and mucus Defecation (diarrhea) and vomiting to expel microbes Highly acidic gastric acid secretions (pH 1.2-3.0) destroy bacteria and toxins. Internal innate immune defences; Antimicrobial substances; 1. Interferons, IFNα, IFNβ, IFNγ, antiviral proteins that inhibit replication of viruses in cells nearby, and limit the spread of the virus. 2. Complement proteins, when activated promote bacterial cytolysis, phagocytosis and inflammation 3. Iron binding proteins, eg transferrin and lactoferrin, inhibit the growth of irondependent bacteria 4. Antimicrobial peptides (AMPs) such as Internal innate immune defences; Cellular defences; 1. Natural killer (NK) cells; kill virally infected cells which have abnormal proteins in the plasma membrane, by releasing perforin (cytolysis) and granzymes (induce apoptosis). Released microbes are killed by phagocytes. 2. Phagocytes; the neutrophils and macrophages are cells specialised to ingest and destroy microbes. A phagocyte engulfing bacteria Phagocytosis (neutrophils and macrophages) Phagosome Phagolysoso me Inflammation neutrophi l The stages of inflammation; vasodilation increased vascular permeability phagocyte emigration tissue repair macropha ge monocyt e The symptoms of inflammation; rubor calor tumor dolor Wound repair in the skin The symptoms of inflammation; rubor calor tumor dolor Pus Acne Conjuctivit Macrophages engulf, bacteria, damaged tissue and worn out neutrophils, but eventually macrophages die too. Pus is a pocket of dead phagocytes and damaged tissue that occurs at most sites of inflammation and persists until the bacteria is cleared. Pus can drain externally (shown) or The mediators of vasodilation and increased vascular permeability; Histamine released from mast cells activated by complement proteins (C3a and C5a) Bradykinin also affect nerve endings and cause pain Prostaglandins Leukotrienes (LTC4) Vasodilation and increased permeability causes oedema, but delivers antibodies and coagulation factors from the blood into tissues to limit the spread of (opsonisatio n) Complement activation in phagocytosis, inflammation and bacterial cytolysis