Innate Immunity PDF

TOPIC: INNATE IMMUNITY LESSONS/CONCEPTS: Epithelial Barriers and Complement Cells of Innate Immunity & Inflammation Innate Recognition of Non-Self and Damage Add...

TOPIC: INNATE IMMUNITY LESSONS/CONCEPTS: Epithelial Barriers and Complement Cells of Innate Immunity & Inflammation Innate Recognition of Non-Self and Damage Add photo Lonnie Lybarger, PhD in [email protected] Master  Learning Objectives 1. Describe the properties of epithelial surfaces that contribute to innate immunity. 2. Describe the roles of complement components in the innate immune response. Explain how the system is triggered and what it does to combat infection. 3. Describe the properties and roles in immunity of key innate cells such as neutrophils and macrophages. 4. Explain the basic pathway of an acute inflammatory response; understanding the roles of key chemical mediators and cell types. 5. Explain the mechanisms used by the innate immune system to recognize “non-self”. Describe the function of Pattern Recognition Receptors, and explain the importance of cellular damage-sensing in innate immunity. Innate immunity - Mechanisms Epithelial surfaces - skin, lungs, GI tract, reproductive tract Complement system - anti-microbial plasma proteins Tissue-resident and circulating immune cells - macrophages, neutrophils, dendritic cells, etc., NOTE #1: innate system potentiated by adaptive components NOTE #2: most cells perform innate immune functions Epithelial surfaces - multilayered protection Mechanism Sites Epithelial cell tight junctions Skin, gut, lung, eye Mechanical Longitudinal flow Gut, urinary tract Mucociliary escalator Lung Low pH Stomach Fatty acids Skin Chemical Anti-microbial enzymes (lysozyme) Tears, saliva, gut Anti-microbial peptides (defensins) Skin, gut, lungs Microbiological Healthy microbiome Skin, gut, respiratory Epithelial surfaces - multilayered protection Potential portals of entry are heavily defended: PHYSICAL HEALTHY LOW SPECIAL SITE CILIA MUCUS sIgA BARRIER MICRIOBIOME pH FACTORS Fatty acids from action Skin +++ – + – – ++ of normal flora on sebum Conjunctiva ++ – – – + – Lysozyme Oropharynx +++ – +++ – + – Upper respiratory tract ++ + +++ ++ ++ – Turbinate baffles Mucociliary escalator, Lower respiratory tract ++ +++ – ++ ++ – alveolar macrophages; cough reflex Stomach ++ – – ++ – +++ Hydrochloric acid Intestinal tract ++ – +++ +++ +++ – Bile; digestive enzymes Urinary tract ++ – – – + + adapted from Sherris, Table 22-1 Epithelial surfaces - multilayered protection Most epithelia have a cell layer(s) with tight junctions Produce many antimicrobial factors Watertight barrier + antimicrobial substances Anti-microbial peptides (e.g. lysozyme), IgA, mucus Mucus power! 2-3 liters of mucus per day Mucus layer = protective coating: GI tract = keeps microbiome away from epithelium Respiratory tract = traps particles Mucins – family of heavily glycosylated proteins - membrane-bound and secreted forms Extremely hydrophilic https://www.sigmaaldrich.com/life-science/biochemicals/biochemical-products.html?TablePage=21735648 Mucus power! Problems with clearance of mucus are devastating What happens when barriers are breached? Epithelial surfaces - skin, lungs, GI tract, reproductive tract Complement system - anti-microbial plasma proteins Tissue-resident and circulating immune cells - macrophages, neutrophils, dendritic cells, etc., Complement system Abundant plasma proteins - function in an enzymatic cascade, leading to: - molecular ‘tagging’ of microbes - help induce inflammatory response Complement system Abundant plasma proteins - function in an enzymatic cascade: i) direct killing of microbes or infected cells – induce lysis ii) opsonize pathogens - promote uptake (phagocytosis) iii) induce inflammation - blood/plasma factors into tissues Complex system of 30+ liver-produced proteins Sequential factors activated, leading to amplification Multiple triggers for activation of the pathway…..  Complement system 3 major ways to get activation: The Immune System, 3ed (Garland). Fig. 2.5 Complement system Mannose-binding lectin example: C2a C4b2b3b MBL C4b2b C4b2b 1) MBL binds pathogen surface, associated MASP-2 cleaves C4 2) C4b coupled to pathogen surface, MASP-2 cleaves C2 3) C4b/C2b are C3 convertase – cleave C3 4) C3b accumulates on pathogen surface – acts as a ‘tag’ - similar activation to the Classical Pathway Janeway’s Immunobiology, Fig 2-20 Complement system Outcomes: Note: relevant cell types express receptors for complement fragments Host cells have inhibitors of complement – prevent host damage adapted from: http://www.medicallibraryonline.com/Complement-System Basic Imm., Fig. 8-11 Complement deficiencies Human deficiencies in most complement components have been described FACTOR DEFICIENCY PHENOTYPE C1q Lupus C2 Sepsis (S. pneumoniae); Most common deficiency in Caucasians C3 Most severe phenotype, sepsis and other problems C4 Lupus, bacterial disease MAC Neisseria infections Complement Kidney damage, other problems regulatory proteins Info adapted from UpToDate.com  QUESTION??? Which of the following are considered host defense mechanisms at epithelial surfaces? Select all that apply. ___ Tight junctions between epithelial cells ___ Antimicrobial factors in the blood/circulation ___ Healthy, diverse microbiome ___ Antimicrobial factors secreted at epithelial surface ___ Low pH in the stomach  QUESTION??? 1) Which of the 3 major pathways of complement activation would be impacted in an individual with defective lymphocyte function, and why? 2) Explain how cleavage of C3 into C3a and C3b fragments can lead to: i) phagocytosis of pathogens ii) lysis of some pathogens iii) activation of the inflammatory response  TOPIC: INNATE IMMUNITY LESSONS/CONCEPTS: Epithelial Barriers and Complement Cells of Innate Immunity & Inflammation Innate Recognition of Non-Self and Damage Add photo Lonnie Lybarger, PhD in [email protected] Master  Learning Objectives 1. Describe the general features that distinguish innate versus adaptive immunity (major cell types, kinetics of response, features of response, receptor families important for response). 2. Describe the properties of epithelial surfaces that contribute to innate immunity. 3. Describe the roles of complement components in the innate immune response. Explain how the system is triggered and what it does to combat infection. 4. Describe the properties and roles in immunity of key innate cells such as neutrophils and macrophages. 5. Explain the basic pathway of an acute inflammatory response; understanding the roles of key chemical mediators and cell types. 6. Explain the mechanisms used by the innate immune system to recognize “non- self”. Describe the function of Pattern Recognition Receptors, and explain the importance of cellular damage-sensing in innate immunity. Phagocytes Macrophages - tissue-resident, can be long-lived - initiate responses, serve many roles - derived from blood monocytes Neutrophils - also called polymorphonuclear (PMN) leukocytes - short-lived (≈1-5 days), abundant in circulation - ‘flood’ into sites of inflammation both cells can kill microbes: digestive enzymes, low pH, reactive oxygen species, etc. Phagocytosis (Neutrophils, Macrophages, Dendritic cells) 1. Receptor-mediated uptake of particles - complement and antibodies help - opsonization! 2. Phagosome fuses with lysosomes 3. Degradation of ingested material Phagocytes endowed with many killing mechanisms Basic Imm., Fig. 2-16 Phagocyte activation – killing mechanisms Ability of phagocytes to kill pathogens depends, in large part, on the production of reactive oxygen species - two key enzymes are NADPH oxidase and myeloperoxidase Deficiency of these enzymes (esp. NADPH oxidases) results in Chronic Granulomatous Disease - frequent, recurrent bacterial and fungal infections Robbins Basic Pathology, 10th Ed., Fig. 3.7 Neutrophils at work: Molecular Biology of the Cell, Sixth Edition https://www.youtube.com/watch?v=pYTHMQi4l84 Mast cells Granulocyte resident in tissue, esp. mucosal surfaces, often near small blood vessels Loaded with granules containing histamine (and many other factors) Respond to many stimuli to induce degranulation - C3a/C5a, microbes, IgE/antigen Causes vasodilation and increases vascular permeability Major role is some allergic responses Cell. and Mol. Imm., 9th Ed., Figs. 2.1, 20.2 Inflammation overview Tissue reaction delivering mediators to location of need 3 basic stages of Acute Inflammation: 1) Dilation of small vessels (arterioles) - increased blood flow to tissue, reduced flow rate 2) Increased permeability of the microvasculature - movement of fluid into tissue 3) Extravasation of leukocytes Generally beneficial, but….. - MAJOR aspect of medicine - common therapeutic target Inflammation - hallmarks Aulus Cornelius Celsus – 1st Century Roman medical writer Rubor - redness Tumor - swelling Calor - heat Dolor - pain https://cnx.org/contents/[email protected]:rFziotaH@5/Introduction Inflammation – Acute vs Chronic Robbins Basic Pathology, 10th Ed., (available through AHSL Library) Acute inflammation – basics *causes edema and lymph flow Basic Imm., Fig. 2-14 Intravital imaging of extravasation https://www.youtube.com/watch?v=LB9FYAo7SJU  QUESTION??? Complete this table: Macrophage Neutrophil Phagocyte? Short lifespan? Relative abundance in blood? Can reside in healthy tissue? Can initiate inflammation?  TOPIC: INNATE IMMUNITY LESSONS/CONCEPTS: Epithelial Barriers and Complement Cells of Innate Immunity & Inflammation Innate Recognition of Non-Self and Damage Add photo Lonnie Lybarger, PhD in [email protected] Master  Learning Objectives 1. Describe the general features that distinguish innate versus adaptive immunity (major cell types, kinetics of response, features of response, receptor families important for response). 2. Describe the properties of epithelial surfaces that contribute to innate immunity. 3. Describe the roles of complement components in the innate immune response. Explain how the system is triggered and what it does to combat infection. 4. Describe the properties and roles in immunity of key innate cells such as neutrophils and macrophages. 5. Explain the basic pathway of an acute inflammatory response; understanding the roles of key chemical mediators and cell types. 6. Explain the mechanisms used by the innate immune system to recognize “non-self”. Describe the function of Pattern Recognition Receptors, and explain the importance of cellular damage-sensing in innate immunity. Inflammation - stimuli/triggers Sterile and non-sterile triggers: Trauma and tissue damage Autoimmune reactions Allergies Foreign bodies - splinters, dirt, sutures Infections, microbial toxins ❖ Triggers vary; responses can be similar Innate recognition - PAMPs How do our cells know that something is ‘foreign’??? Conserved molecular structures on classes of microbes Examples: - bacterial membrane lipids - bacterial/fungal cell wall components - viral and bacterial nucleic acids These are all examples of Pathogen-Associated Molecular Patterns (PAMPs) Innate recognition - DAMPs How do our cells know that something is ‘wrong’??? Presence of cell and tissue damage - Stuff (molecules) where it shouldn’t be Examples: - Extracellular heat-shock proteins - Lysosomal enzymes in cytosol - Nuclear components in cytosol - Mitochondrial DNA in cytosol - Extracellular ATP These are all examples of Damage-Associated Molecular Patterns (DAMPs) Examples of PAMPS and DAMPs Cellular and molecular immunology, 9th Ed., (available through AHSL Library) Receptors for PAMPs and DAMPs Receptors for PAMPs and DAMPs typically expressed by innate immune cells, called Pattern Recognition Receptors (PRRs) Expressed by leukocytes, and some other cells types Key point: PRRs used to survey different compartments of the cell/body There are many types of PRRs Leads to activation of cells Generally, induce proinflammatory genes Basic Imm., Fig. 2-2 Pattern recognition receptors - TLRs Toll-Like Receptors (TLR) - recognize extracellular microbial ligands - 10 TLRs in human Ligands mostly of microbial origin Leads to activation of cells Generally, induce proinflammatory genes Basic Imm., Fig. 2-3 Pattern recognition receptors - NLRs NOD-like receptors (NLR) - cytosolic pattern recognition receptors - Activated by PAMPS and DAMPs - 22 family members in human; more in mice - Some active NLRs form the ‘inflammasome’ complex, leading to IL-1 release from cells - Some active NLRs induce secretion of other cytokines Basic Imm., Fig. 2-5 Cytokines Many are interleukins, IL-1, -2, -3, etc. Important pharmacologic targets https://openstax.org/details/books/microbiology Cytokines Small proteins (15-25 kDa) Function in autocrine, paracrine, and/or endocrine fashion Direct the activities of other cells >50 in humans Important therapeutic targets ❖ Our focus will be on those mentioned in the context of certain pathways and processes in the block Cytokines - a sampling PRINCIPAL ACTIONS IN CYTOKINE PRINCIPAL SOURCES INFLAMMATION IN ACUTE INFLAMMATION Stimulates expression of endothelial Macrophages, mast cells, T adhesion molecules and secretion of TNF lymphocytes other cytokines; systemic effects; macrophage activation Macrophages, endothelial cells, IL-1 Similar to TNF; greater role in fever some epithelial cells Systemic effects (acute phase IL-6 Macrophages, other cells response) Macrophages, endothelial cells, Recruitment of leukocytes to sites of CHEMOKINES T lymphocytes, mast cells, inflammation; migration of cells in other cell types normal tissues Recruitment of neutrophils and IL-17 T lymphocytes monocytes IN CHRONIC INFLAMMATION IL-12 Dendritic cells, macrophages Increased production of IFN-γ Activation of macrophages (increased IFN- γ T lymphocytes, NK cells ability to kill microbes and tumor cells) Recruitment of neutrophils and IL-17 T lymphocytes monocytes Adapted from Robbins and Cotran, 9th Ed., Table 3-6  QUESTION??? PRRs can recognize PAMPs and DAMPs. Classify the following as either PAMP or DAMP: ___ Uric acid crystals (cause of gout) ___ Lipopolysaccharide from bacterial outer membrane ___ Proteins from flagellum of bacteria ___ Double-stranded viral RNA ___ Nuclear DNA in the cytoplasm ___ Extracellular ATP ___ Actin molecules in extracellular space