BMF_Innate Immunity 2023 PW.pptx
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16th November 2023 Innate Immunity Dr Patrick Walsh Class Year 1 Module BMF Title Innate Immunity LECTURE LEARNING OUTCOMES At the end of this lecture you should be able to: RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H • Outline the innate immune response • Explain the mechanism...
16th November 2023 Innate Immunity Dr Patrick Walsh Class Year 1 Module BMF Title Innate Immunity LECTURE LEARNING OUTCOMES At the end of this lecture you should be able to: RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H • Outline the innate immune response • Explain the mechanism of phagocytosis • Describe the process of inflammation and the role of inflammatory mediators • Illustrate the MHC class I and class II antigen presentation pathways • Describe the function and activation of the complement pathway • List diseases associated with innate immune dysfunction Dr Chiara De Santi, Innate Immunity OUTLINE OF THE INNATE IMMUNE RESPONSE • Responds RAPIDLY to microbes or damage RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H • Broadly distinguishes self from non-self • Eliminates pathogens by inducing processes such as Phagocytosis and Inflammation • Acts as an alarm system by releasing cytokines and chemokines • Communicates directly with the adaptive arm of immunity to inform it of ‘type’ of threat using antigen presentation • Involves soluble components such as complement Dr Chiara De Santi, Innate Immunity WHAT TRIGGERS AN INNATE IMMUNE RESPONSE? Breaching barriers T H E W O R L D T O B E T T E R H E A LT H • Tissue injury regardless of type can cause inflammation – Splinter – Cut +/- infection – Insect bite – Trauma RCSI LEADING • Microbes when breach the barrier cause inflammation Recognition by Innate Immune Cells Dr Chiara De Santi, Innate Immunity Microbe and damage recognition by immune cells T H E W O R L D T O B E T T E R H E A LT H • Microbes have regular patterns of molecular structure that are recognised by innate immune cells termed ‘pathogen-associated molecular patterns’ (PAMP) microbes Release of self molecules • Macrophage, neutrophils and dendritic cells express a number of receptors that allow them to recognise different pathogens collectively called ‘Pathogen Recognition Receptors’ (PRR) Activation of Innate immune cells RCSI LEADING • Cells when damaged release self molecules – Damage-associated molecular patterns’ (DAMPs) • Activation of innate immune cells – what are these?? Which ones are tissue resident??? Dr Chiara De Santi, Innate Immunity T H E W O R L D T O B E T T E R H E A LT H INNATE IMMUNE CELL ACTIVATION LEADS TO 3 FUNDAMENTAL CELLULAR Innate PROCESSES immune cell activation Cellular Process Phagocytosis Cytokine ProductionAntigen Presentation Key Function RCSI LEADING Destroy Pathogen Dr Chiara De Santi, Innate Immunity Inflammation Activate T cells RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H Phagocytosis engulfs and kills microorganisms • Macrophages and neutrophils express receptors that bind to microbes • Microbes are engulfed into phagosomes • Lysosome fuses with the phagosome • The microbes are killed in the phagolysosome by toxic substances: - NO (nitric oxide) is made by iNOS (nitric oxide synthase) - ROS (reactive oxygen species) is made by phagocyte oxidase (also known as NADPH oxidase) – respiratory burst - Lysosomal proteases break down microbial proteins • Neutrophils are short lived, macrophages long-lived (NADPH oxidase) D r C h i2-18 a r a DBasic e S a nImmunology, ti, Innate Imm u nEdition, ity Figure 6th Abul Defects in the NADPH oxidase system – Chronic Granulomatous Disease RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H • Phagocytes don’t function properly • Due to a defect in NADPH oxidase • 65-70% of cases are X-linked so more frequent in males • First appears in childhood and leads to frequent and severe bacterial and fungal infections • Most common infections occur in lungs, skin, liver and lymph nodes • Formation of granulomas, which form during when microbes cannot be cleared • inflammation Diagnostic test for CGD is the Dihydrorhodamine (DHR) assay – Whole blood is taken and neutrophils tested for the conversion of DHR to fluorescent rhodamine which only occurs in the presence of ROS. Dr Chiara De Santi, Innate Immunity T H E W O R L D T O B E T T E R H E A LT H INNATE IMMUNE CELL ACTIVATION LEADS TO 3 FUNDAMENTAL CELLULAR Innate PROCESSES immune cell activation Cellular Process Phagocytosis Cytokine ProductionAntigen Presentation Key Function RCSI LEADING Destroy Pathogen Dr Chiara De Santi, Innate Immunity Inflammation Activate T cells T H E W O R L D T O B E T T E R H E A LT H KEY SIGNS OF INFLAMMATION RCSI LEADING Aulus Cornelius Celsus 1st Century AD Dr Chiara De Santi, Innate Immunity WHAT IS THE ROLE OF INFLAMMATION? 1. Respond to infection/insult/injury T H E W O R L D T O B E T T E R H E A LT H 2. Bring immune cells to site so they can fight it 3. Localise the infection and protects the body from further infection/injury 4. Increases production of protective proteins RCSI LEADING 5. Promote tissue repair and resolution of infection Dr Chiara De Santi, Innate Immunity RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H KEY STAGES OF INFLAMMATION Tissue Injury, Breech in Barrier, Microbe entry Dr Chiara De First Step Recognition via PRR Release of S a n t i , I ninflammatory nate Immunity – Second Step Vasodilation Permeability Cell Adhesion Third Step Extravasation Key stages of Inflammation – First STEP RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H Tissue Injury Microbes proteins • Recognition by tissue resident innate immune cells - Macrophages - Dendritic Cells lipids • Induction of Phagocytosis - Engulf and destroy microbe (macrophage) - Antigen presentation (dendritic cells) • Release of Inflammatory Mediators First Step Recognition via PRR - Cytokines (IL-1, TNF) and chemokines (IL-8) Release of inflammatory mediators - Lipids (Prostaglandins, Leukotrienes, PAF) Dr Chiara De Santi, Innate Immunity Key stages of Inflammation – Second STEP T H E W O R L D T O B E T T E R H E A LT H • - Vasodilation increase diameter of blood vessels increased blood flow decreased velocity • Permeability - endothelial cells lining blood vessels become ‘leaky’ - enables influx of soluble protein (C5a) - influx of fluid which enables migration RCSI LEADING • - Dr Cell adhesion endothelial cells are activated increase cell adhesion molecules promotes binding of circulating immune cells (‘rolling’) Chiara De Santi, Innate Immunity Redness Swelling Heat Second Step Vasodilation Permeability Cell Adhesion Key stages of Inflammation – Third STEP Extravasation • - neutrophils first - then monocytes T H E W O R L D T O B E T T E R H E A LT H • Activation of Neutrophils - Phagocytosis - Destruction of microbe • Activation of Monocytes - Differentiation into macrophages - Release of more inflammatory mediators (cytokines, chemokines, lipids, proteins) - Maintains inflammation RCSI LEADING • Activation of Mast cells - Release histamine NO Third Step Extravasation Redness, Swelling, Heat, Pain Dr Chiara De Santi, Innate Immunity H E A LT H THE WORLD TO BETTER RCSI LEADING Dr Chiara De Santi, Innate – https://www.youtube.com/watch?v=Ys6Rl Immunity T H E W O R L D T O B E T T E R H E A LT H EXTRAVASATION 3 2 RCSI LEADING 1 Figure 2.17 Basic Immunology, 6th Edition, Abul K. Abbas Dr Chiara De Santi, Innate Immunity 4 RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H EXTRAVASATION Dr 1. Upon microbe detection, macrophages release cytokines (IL-1, TNF) and chemokine (IL-8) 2. IL-1 and TNF causes endothelial cells express selectin which binds to carbohydrate on leukocyte cell surface (rolling adhesion) 3. a) IL-8 displayed on luminal surface of endothelial cells helps the adhesion of circulating leukocytes (who express chemokine receptors). b) This stimulates integrin on the leukocytes to switch from a low affinity state to a high affinity state. c) This leads to a firm binding/arrest of the rolling leukocytes (stable/tight adhesion) 4. Leukocytes migrate through the vessel wall and follow Chiara De Santi, Innate Immunity Inflammatory mediators all work together Damaged epithelium, resident macrophages, dendritic cells and mast cell produce: T H E W O R L D T O B E T T E R H E A LT H •Vasodilators (nitric oxide, prostaglandins) to increase the diameter of the blood vessels •Permeabilisers (IL-1, histamine and prostaglandins) cause endothelial cells lining the capillaries and blood vessels near the sit of infection to become ‘leaky’ - induce an influx of cells, fluid and proteins RCSI LEADING •Cell activators inflammatory cytokines (IL-1, TNF) promote recruitment, sustained activation, upregulate adhesion molecules Dr •Chemoattractants (IL-8) bring more immune cells to the Chiara De Santi, Innate Immunity Systemic effects of cytokine release T H E W O R L D T O B E T T E R H E A LT H Hypothalamus RCSI LEADING Liver Dr Chiara De Santi, Innate Immunity RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H Role of Chemokines • Chemokines are released by damaged cells and immune cells • IL-8 is a key chemokine important in inflammatory response • Function: bring more cells (particularly neutrophils) to infected region ‘Chemoattractants’ • Increase expression of adhesion molecules on immune cells • Released locally in high concentrations • Cells with receptors respond – move up concentration gradient Dr Chiara De Santi, Innate Immunity Chemokines Neutrophil Chemotaxis http://www.youtube.com/watch?v=ZUUfdP87Ssg&eurl=htt p://www.freesciencelectures.com/video/neutrophil-chemot Resolution of Acute Inflammation T H E W O R L D T O B E T T E R H E A LT H Must actively terminate inflammation to prevent bystander destruction of tissues RCSI LEADING Mechanisms of resolution: • Short half life of neutrophils and inflammatory mediators • Macrophages will change character and promote repair, releasing inhibitory cytokines (IL-10 and TGF-b) to limit inflammation • Macrophages also release growth factors (FGF) to which acts on fibroblasts to promote repair • Lipid mediators – switch to production of antiinflammatory lipoxins, resolvins, and protectins Dr Chiara De Santi, Innate Immunity RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H Acute vs chronic inflammation Dr Chiara De Chronic Inflammation of prolonged duration in which active inflammation, tissue injury and healing proceed simultaneously eg. persistent infection (eg. hepatitis, tuberculosis), toxic agents (eg. silica), autoimmune reactions (eg. rheumatoid arthritis, multiple Santi, Innate Immunity sclerosis, lupus) Which of the following cytokine recruits neutrophils to the site of infection (‘chemoattractant’)? A. IL-8 B. IL-2 C. IL-10 Which of the following is produced in the phagolysosome to kill bacteria? A. Histamine B. Reactive Oxygen species (ROS) C. TNF THE COMPLEMENT SYSTEM T H E W O R L D T O B E T T E R H E A LT H The complement system consists of several plasma proteins that work together to: RCSI LEADING • Promote inflammation • Opsonisation and Phagocytosis • In some cases, kill the microbes Innate immune mechanism Non-specific Dr Chiara De Santi, Innate Immunity THE COMPLEMENT SYSTEM T H E W O R L D T O B E T T E R H E A LT H • Collection of circulating and membrane associated proteins (20+)(C, complement) • The complement system is initiated by three different pathways RCSI LEADING • They are proteolytic enzymes, which work in an enzymatic cascade • The products perform the effector functions of complement Dr Chiara De Santi, Innate Immunity THE COMPLEMENT SYSTEM C1 RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H The pathogenic antigen (such as LPS) activates C3 so it creates a C3B complex. Dr Chiara De Santi, Innate Immunity – Figure 2.14, Basic Immunology, 6 th ed. Abul Abbas 1. Promote inflammation RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H C3a, as well as C5a fragments, are important inflammatory activators: • Act as chemoattractants for neutrophils, monocytes • Stimulate the release of inflammatory mediators from various immune cells • Enhance vasodilation and vascular permeability Dr Chiara De Santi, Innate Immunity – Figure 13.17, Cellular and Molecular Immunology, 10th ed. Abul Abbas 2. Opsonisation and Phagocytosis C3b is deposited on surface of microbes Acts as an opsonin to tag bacteria for recognition by phagocytes C3b is recognised by Complement Receptor (CR) of phagocytes Phagocytosis is triggered T H E W O R L D T O B E T T E R H E A LT H • • • RCSI LEADING • Dr Chiara De Santi, Innate Immunity – Figure 13.17, Cellular and Molecular Immunology, 10th ed. Abul Abbas RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H 3. Membrane Attack Complex Dr Chiara De • Late steps of complement occur when C5b binds to C6-C9 • This causes C9 to polymerise and from a pore - membrane attack complex • Loss of cell integrity where water and ions enter • Causes death of certain microbes (Neisseria particularly Santi, Innate Immunity Complement deficiencies RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H • Rare 1- 2% of immunodeficiencies • C3 Deficiency is linked with frequent pyogenic (pus-forming) infection in infants and young children and severe pyogenic bacterial infections in adults. • Deficiency in some early components (eg C2 and C4) are associated with an increase of immune complex-mediated autoimmune disease (eg systemic lupus erythematosus) • Deficiency in terminal pathway (C5-C9): The lack of MAC formation results in severe recurrent infections by Neisseria gonorrhoeae or Neisseria meningitidis. • Deficiency in C1 INH causes a disease called hereditary angioedema Dr Chiara De Santi, Innate Immunity T H E W O R L D T O B E T T E R H E A LT H INNATE IMMUNE CELL ACTIVATION LEADS TO 3 FUNDAMENTAL CELLULAR Innate PROCESSES immune cell activation Cellular Process Phagocytosis Cytokine ProductionAntigen Presentation Key Function RCSI LEADING Destroy Pathogen Dr Chiara De Santi, Innate Immunity Inflammation Activate T cells ANTIGEN PRESENTATION en g o h Pat uction tr des T H E W O R L D T O B E T T E R H E A LT H Pathogen Pathogen internalisatio n Ki n lli g of ed ll t ec ce f in MHC T cell RCSI LEADING Antigen presentation INFECTED Cell Dr Chiara De Santi, Innate Immunity pro T ce li diff feratioll ere ntia n and t io n Cytotoxicit y, Cytokine secretion TCR Effector T cells There are two antigen presentation pathways RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H Depends on route by which antigen enters the cell Dr The antigen is internal (viral infection) The antigen is external (phagocytosis of bacterial antigens) Any cell can be target – all nucleated cells express MHC class I Only phagocytic cells involved – only they express MHC class II Chiara De Santi, Innate Immunity MHC class I Presentation Performed by all nucleated cells T H E W O R L D T O B E T T E R H E A LT H Virus MHC class I TCR Antigen T Cytotoxic T Cell RCSI LEADING Epithelium Endothelium Fibroblasts (all nucleated cells) Dr Chiara De Santi, Innate Immunity MHC class I Presentation - Performed by all nucleated cells T H E W O R L D T O B E T T E R H E A LT H • Also known as Class I pathway • Constantly presenting self-peptides, cancer antigens or antigens from derived from viruses or intracellular bacteria • Proteins are digested into peptides by the proteasome • Peptides transported into the endoplasmic reticulum • Loaded onto MHC class I in ER and transported to cell surface RCSI LEADING Endoplasmic Reticulum Dr Chiara De Santi, Innate Immunity – Figure 3.12, Basic Immunology, 6 th ed. Abul Abbas MHC Class II Presentation T H E W O R L D T O B E T T E R H E A LT H MHC class II Antigen TCR T Helper Cell RCSI LEADING Antigen Presenting Cell (APC) Dendritic Cell Macrophage B cells Dr Chiara De Santi, Innate Immunity MHC class II Presentation - Performed by APC RCSI LEADING T H E W O R L D T O B E T T E R H E A LT H • Also known as Class II pathway • Pathogens, toxins, fragments that have been endocytosed/phagocytosed • Proteins digested to peptides in the endosome/lysosome • MHC class II is transported with its Ii from ER to the late endosome/lysosome • Peptides are loaded onto the MHC class II molecule and exported to the cell surface Dr Chiara De Figure 3.12, Basic Immunology, 6 th ed. Abul Abbas Santi, Innate Immunity SUMMARY OF THE INNATE IMMUNE RESPONSE • Occurs at the portal entry for microbes – Epithelia barriers of skin, gastro and respiratory tracts T H E W O R L D T O B E T T E R H E A LT H • In the tissues – Resident macrophages, dendritic cells and mast cells – Initiate phagocytosis and inflammation • In the blood – Plasma proteins such as complement – Neutrophils are recruited from blood to site of infection RCSI LEADING • In the lymph nodes Dr – Dendritic cells travel from site of infection to lymph nodes – Antigen presentation to T cells Chiara De Santi, Innate Immunity 3rd October 2022 Thank you Dr Patrick Walsh Class Year 1 Module fortitle Practice Click toFoundations edit master style1 Title Innate Immunity
