Innate Immunity I - Immediate Response PDF

Defense Against the Dark Arts (Immunology) harry potter symbol - Bing images defense against the dark arts - Bing images Randal Gregg, PhD 1 Innate Immunity I Randal Gregg, PhD Immediate Response harry potter symbol - Bing images defense against the dark arts - Bing images 2 Learning Objec...

Defense Against the Dark Arts (Immunology) harry potter symbol - Bing images defense against the dark arts - Bing images Randal Gregg, PhD 1 Innate Immunity I Randal Gregg, PhD Immediate Response harry potter symbol - Bing images defense against the dark arts - Bing images 2 Learning Objectives 1) Identify the physical barriers which protect against pathogenic microbe colonization. 2) Identify the major chemical barriers of innate immunity and distinguish the mechanisms of action of each. 3) Define the role of the microbiota in innate immunity. 4) Define the major components of alternative C3 and C5 convertases and identify their functions. 5) Identify the three major functions of complement activation and define the complement components and cells involved. 6) Distinguish between the regulatory factors involved in the inactivation of complement. 3 First Line of Defense (Physical and Chemical Barriers) harry potter using petronis charm background - Search Images (bing.com) Physical barriers Epithelial cells of the skin and the mucosal surfaces that line the digestive, respiratory and urogenital tracts form a physical barrier between environmental microbes and the host • Tight junctions between the epithelial cells block microbial passage • Stratum corneum (outer layer of the skin) flakes off thereby removing adherent microbes • Mucus captures pathogens and foreign agents – removed by ciliary action in the bronchial tree along with sneezing and coughing (peristalsis in the gut, vomiting and diarrhea remove agents from GI tract) 5 Chemical barriers Defensins are human antimicrobial peptides (AMP), 35-40 aa rich in Arg, with both hydrophilic and hydrophobic regions • Defensins penetrate microbial membranes and disrupt their integrity leading to lysis • Two types = human alpha and beta defensins (HAD, HBD) • Constitutively secreted at mucosal surfaces to maintain levels of microbiota • Produced by Paneth cells in intestinal crypts as well as epithelial cells and neutrophils • Defensins function poorly in physiological conditions but operate best in sweat, tears, gut lumen and the phagosome 6 Chemical barriers Pentraxins are cyclic proteins that circulate in the blood and lymph and bind to pathogen surfaces and serve as a target site for phagocyte attachment • Phagocytes possess receptors that bind to pentraxins that are attached to the pathogen surface • Upon binding, phagocytes engulf and destroy the attached pathogen • Production in the liver is induced by IL-6 and locally in tissues by infiltrating immune cells upon innate receptor activation CRP = C reactive protein SAP = serum amyloid P PTX3 = pentraxin 3 7 Chemical barriers Lysozyme is an enzyme found in saliva, tears, mucus, plasma, tissue fluids as well as phagocytic granules which operates to destroy bacterial cell walls • Bacterial cell wall peptidoglycan is composed of repeating amino sugars, N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) crosslinked by peptide bridges • Lysozyme hydrolyzes the 1,4 beta linkages between NAG and NAM increasing permeability and causing the bacteria to burst PEPTIDOGLYCAN 8 Chemical barriers Phospholipase A2 • Enzyme that penetrates the bacterial cell wall and hydrolyzes the membrane phospholipids Cathelicidins • Cationic peptides that form transmembrane pores in microbial cell membranes Lactic and Fatty Acids • Found in perspiration and sebaceous secretions; disrupt electron transport chain and oxidative phosphorylation as well as enzyme activity and nutrient uptake (cell membrane targeted) Lactoferrin and Transferrin • Found in body secretions, plasma and tissue fluid, sequester iron for use by human cells and not bacteria Hydrochloric Acid • Found in gastric secretions which destroy the membranes of swallowed bacteria UREA has antibacterial activity 9 Microbiota as a barrier • Before birth, mammalian babies have no commensal microbes • Starting at birth and contact with the mother’s vagina, the infant’s skin and mucosal surface begins to colonize commensal microorganisms from family, friends and pets • Many of the commensals have coevolved with placental mammals and developed symbiotic relationships with their hosts • Direct evidence of the benefit of having and maintaining commensals is the poor health of lab mice kept in a germ-free environment • Aspiring pathogens must compete with the well adapted commensals for nutrients and space • Highest density of bacteria is present in the large intestine (up to 1013) and area of the lowest oxygen concentration (anaerobic life) • Westernized diet (high saturated fats, high sugar, low fiber) thought to reduce microbiome diversity while increased fiber intake is associated with increased diversity (more diversity, less inflammation) • Aging lowers microbiome diversity as does a reduction in physical activities such as exercise 10 Microbiome changes with development Up to 80% of immune cells reside in the gut epithelium – first line of defense against harmful agents 11 Chemical barrier – Complement system Complement is a collection of >30 proteins constitutively made by the liver and present in the blood, lymph and extracellular fluids • As soon as a pathogen penetrates the epithelial barrier – complement is activated • Complement proteins coat the bacterial surface and extracellular viral particles to make them more easily phagocytosed (esp. encapsulated bacteria) • Many bacteria can resist phagocytosis otherwise • Complement proteins are produced as zymogens, upon activation, these proteases cleave proteins in a series • 3 functions of complement activation: o Microbial lysis o Inflammation o Enhanced phagocytosis (opsonization) 12 Complement component 3 (C3) • C3 is released from the liver in an inactive form • The thioester bond is sequestered • C3 can either undergo a spontaneous conformation change – or – be cleaved to expose the thioester bond • Nucleophilic attack can occur by H2O (most often) – or – amino (R-NH2) / hydroxyl (R-OH) groups of proteins/carbs on pathogen surface • C3b binds to the pathogen proteins/carbs and is termed complement fixation K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 13 Alternate pathway of complement activation Occurs in the blood and tissues (early complement response) 1 2 3 4 C3 convertase 1 2 3 4 C3 undergoes a spontaneous conformation change in the aqueous environment of the blood/tissues – thioester bond attaches C3 to H2O → iC3 The amount of iC3 increases near the surface of the pathogen (but not attached to the pathogen) iC3 binds to Factor B iC3 bound Factor B is cleaved by Factor D → Ba (released) + Bb (bound to iC3) = iC3Bb iC3Bb effectively cleaves C3 → C3a (released) + C3b (attaches to pathogen surface) = function of a C3 convertase K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 14 Alternative C3 convertase generation • Pathogen-bound C3b binds Factor B and promotes cleavage by Factor D • C3bBb is a potent C3 convertase • C3bBb is attached to the pathogen surface while iC3Bb can diffuse away from the surface • Pathogen now becomes coated with C3b K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 15 Properdin (Factor P) enhances alternative C3 convertase activity Properdin stabilizes the alternative C3 convertase complex (C3bBb) and prevents degradation by other proteases K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 16 Factor H decreases the number of alternative C3 convertase complexes • Factor H binds to C3b together with Factor I → C3b is cleaved to iC3b which cannot form C3 convertase • Patients with a deficiency of Factor I = unregulated C3bBb complexes → depletes C3 → patients more susceptible to infections by encapsulated bacteria (ear infections and abscesses common) K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 17 Factors to block complement activation • DAF (Decay-accelerating factor) and MCP (Membrane cofactor protein) are membrane proteins on the surface of human cells • DAF binds to C3b and dissociates Bb to inactivate the C3 convertase • MCP binds to C3b and recruits Factor I for the cleavage of C3b into iC3b • Factor H can also bind to sialic acid on human cells and recruit Factor I to cleave C3b – Streptococcus pyogenes and Staphylococcus aureus cover their cells with sialic acid to inactivate complement K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 18 First Line of Defense (Initial Cellular Response) harry potter using petronis charm background - Search Images (bing.com) First line of cellular defense - Macrophages • First effector cells that a pathogen encounters upon invasion is the resident macrophages (and tissue epithelial cells) • Found in connective tissues, linings of the GI and respiratory tracts, brain, alveoli of the lungs and the liver (Kupffer cells) • Long-lived phagocytic cells 20 Macrophages express complement receptors CR1 (Complement receptor 1) is expressed on macrophages to facilitate receptormediated phagocytosis also called opsonization K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 21 Complement-CR1 opsonization Ligation of CR1 with C3b activates the phagocytic process in macrophages CR1 can also disrupt any C3 convertase that may have deposited on the macrophage surface K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 22 Complement-CR1 opsonization Ligation of CR1 with C3b promotes uptake of the bound bacterium by an endocytic vesicle CR3 and CR4 can also bind to iC3b fragments to promote opsonization K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 23 Complement-CR1 opsonization When the membrane is fused together the vesicle is now termed a phagosome H+ ions are pumped into the phagosome through channels in the phagosome membrane to reduce the pH K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 24 Complement-CR1 opsonization Lysosomes containing hydrolytic enzymes fuse with the phagosome to form the phagolysosome The enzymes are activated by the low pH in the phagolysosome and destroy the bacterium K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 25 Macrophages express complement receptors that enhance phagocytosis K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 26 C3b initiates the next function of complement activation • C3b also begins to bind to alternative C3 convertase creating a new enzyme complex, alternative C5 convertase (C3b2Bb) • Function of C3b2Bb = C5 is then cleaved into C5a and C5b fragments K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 27 C5b initiates formation of the Membrane Attack Complex (MAC) to directly lyse pathogens Membrane attack complex • C5b binds to C6 → forms a stable complex with a binding site for C7 • C7 binds to C5bC6 → a hydrophobic region of C7 is exposed for initial attachment to the pathogen membrane • C8 binds to C5bC6C7 → a hydrophobic region of C8 is exposed that inserts into the pathogen membrane • C9 monomers assemble binding to C8 and spanning the membrane → osmotic lysis of the pathogen K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 28 Complement deficiencies and disease Complement protein Effects of deficiency C3 Factor I Increased susceptibility to encapsulated bacteria; recurrent infections C5-C9 Increased susceptibility to Neisseria bacterial species (gonorrhea and meningitis); recurrent infections Factor D Properdin (factor P) Increased susceptibility to both encapsulated bacteria and Neisseria species • Complement is most effective against encapsulated bacteria – capsules prevent phagocyte capture and uptake • Deficiencies of complement components often associated with a higher susceptibility to infections with encapsulated bacteria (or other encapsulated microbes) 29 Factors to block alternative C5 convertase activity in human cells Protectin (CD59) • Prevents the recruitment of C9 monomers to the C5bC6C7C8 complex • Homologous restriction factor (HRF) operates the same way S protein • Prevents C7 interaction with the cell membrane • Clusterin and Factor J operate the same way Factors that block complement activity in human cells are linked directly to the plasma membrane, disruption of this connection can lead to a disease called paroxysmal nocturnal hemoglobinuria where red blood cells are lysed by complement. 30 C3a and C5a promote inflammation • During complement activation, two smaller fragments, C3a and C5a, are generated • Main function of C3a and C5a is to promote inflammation • o Promote degranulation of mast cells and basophils in tissues o Granule contents act to increase vascular permeability and promote vasodilation (histamine) o This process increases recruitment of neutrophils and monocytes from the blood to the site of inflammation o Granule contents can can increase CR on phagocytes and promote contraction of visceral smooth muscle (close airway and promote peristalsis) Too much C3a and C5a can induce “systemic” inflammation (anaphylactic shock) so they have been called anaphylatoxins (C5a>C3a) K. Murphy. 2015. Janeway’s Immunobiology. Garland Science. 31 Anaphylactic shock ALLERGENS Drugs • Antibiotics (penicillins) • Anesthetics (lidocaine, procain) Increased vascular permeability Vasodilation EDEMA DECREASED BLOOD PRESSURE Smooth muscle contraction Increased gland secretion WHEEZING DYSPNEA ASPHYXIATION MUCUS Foods and additives • Nuts, seeds • Fish, shellfish • Milk, eggs • Aspartame • Monosodium glutamate Insect and snakes (stings and bites) Latex and other substances ISCHEMIC SHOCK (cells with inadequate O2) 32 Questions? hogwarts dining hall wallpaper - Bing images 33 Next… Innate immunity II Receptors and Cytokines Hogwarts Express Wallpaper (65+ images) (getwallpapers.com) 34