Lecture 9: Innate Immunity Edith Porter, M.D. 1

 Concept of immunity ▪ Innate immunity ▪ Adaptive immunity  Innate immunity: first line of defense ▪ General aspects ▪ Physical factors ▪ Chemical factors ▪ Normal microbiota ▪ Cellular elements ▪ Epithelial cells ▪ Phagocytes ▪ Effector molecule ▪ Complement ▪ Antimicrobial peptides ▪ Interferons ▪ Iron binding proteins  Acute inflammation 2

INNATE IMMUNITY  Functional at birth  Rapid responses: preformed or available within hours after infection  Limited specificity: pattern recognition via toll like receptors  Widely present in nature including in plants, invertebrates and vertebrates ADAPTIVE IMMUNITY Acquired, available within days High specificity Memory In higher vertebrates 3

First Line of DefenseSecond Line of Defense NK cells 4

 Outer body surface  Keratin barrier  Epithelial cell shedding  Dryness 5

 Inner body surfaces  Mucus  Viscous  Protects underlying cells  Contains antimicrobial factors ▪ Lysozyme  Constant fluid flow  Tears  Saliva  Intestinal peristaltic  Urine production and urination  Vaginal secretions  Mucociliary clearance ▪ 1 – 3 cm/h  Epithelial cell shedding 6

 Sebum, unsaturated fatty acids  “antimicrobial lipids”  Low pH  Skin (pH 3-5)  Stomach (pH 1.5 – 3)  Vagina (pH 3 – 5)  Urine (pH 6) 7 o/Acne/images/normal.jpg

 Competes with potential pathogens for nutrients  Directly inhibits potential pathogens  Lactobacilli: lactic acid, low pH  Bacteriocins Skin Tongue Esophagus 8

 Epithelial Cells  Leukocytes 9

10 Keratinizing in skinNon-keratinizing elsewhere

 Express toll-like receptors (TLR 1 –10) that recognize specific pathogen associated molecular patterns (PAMP)  LPS  PG  Produce antimicrobial peptides (AMP)  Kill microbes  Secrete pro-inflammatory cytokines  Alert the host 11

TLR Microbial Products (LPS, PG, etc) Antimicrobial Peptides Cytokines 12

13 Granulocytes MonocytesLymphocytes Natural Killer Cells Anti-viralAnti-bacterial Anti-fungal Anti-parasitic Anti-allergic Anti-bacterial Anti-fungal B-Ly : antibody production T-Ly: orchestrate Anti-parasitic Anti-allergic neutrophil eosinophil basophil

14 Macrophage in bone marrow Dendritic cell Mast cell Anti-parasitic Allergic responses Communicates with lymphocytes Clears bacteria and fungi in tissues

 All originate from bone marrow (red bone marrow)  Circulate in the body through vascular system and lymphatic system  Enter tissue as needed  Some differentiate here and remain in the tissue: macrophages, dendritic cells 15

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Performed by phagocytes (professional eaters) Neutrophils Monocytes  Macrophages Refers primarily to the uptake of bacteria and fungi Relatively inefficient without special opsonins Opsonins are molecules that enhance phagocytosis Make “food more edible” Host derived molecules that cover the microbe and are recognized by phagocytes 17

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 Chemotaxis  Opsonization  Adherence (attachment)  Ingestion (engulfment)  Pseudopods  Phagosome  Phagolysosome  Killing and digestion 20

Chemical attraction of phagocytes to microorganisms and movement of phagocytes towards the source of infection Induced by chemoattractants: Microbial products (formyl-methionine-peptides) Complement Cytokines (“Chemokines”) 21

 Phagocytes need their food (microorganisms) served on silver plates  Opsonines significantly enhance microbial uptake by phagocytes  Cover microbial surfaces and are recognized by specific receptors on phagocyte surfaces  Examples are:  Antibodies  Complement 22

 Oxygen dependent  Oxidative Burst  Reactive oxygen and reactive nitrogen intermediates  Oxygen-independent  Antimicrobial peptides  Low pH  Enzymes (Hydrolases, proteases, phopholipases) 23

 Complement system  Kills and helps in phagocytosis  Antimicrobial Peptides:  Kill  Interferons  Strengthen basic host cell defenses  Iron binding proteins  Expressed by both host and microbe  Competition for iron 24

 System of over 30 serum proteins  Active components (C-) and inhibitors  Widely distributed in body  Many cells can synthesis complement factors  Major producers:  Hepatocytes (liver cells)  Monocytes/macrophages  Fibroblasts 25

 Early events: proteolytic cascade generates bioactive cleavage fragments  C1  C4  C2  C3  C5  C6  C7  C8  C9n  Late events: Protein polymerization generate a pore on target cell 26

 Classical pathway  Antibodies bound to microbes change conformation and open up binding sites for C1  Lectin pathway  Sugar-binding molecule with similar structure to C1 binds to the microbe and activate complement C2 and C4  Alternative pathway  C3 binds directly to the microbial surface aided by factors B, D, and P and activates C5 27

28  Always the same  Pore formation on microbe and direct killing (C5b- C9n)  Opsonization and improved phagocytosis (C3b)  Inflammation and recruitment of phagocytes (C5a, C3a, C4a)

Figure 16.9 (3 of 5) 29

Action on blood vessels and Mast cells Dilation  reddening and heat Leakage of blood components  edema Make endothelial cells and leukocytes sticky Transmigration of leukocytes  pus Chemoattractant for leukocytes 30

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1) Innate immunity is A) The body's ability to ward off diseases. B) The body's defenses against any kind of pathogen. C) The body's defense against a particular pathogen. D) The lack of resistance. E) Increased susceptibility to disease. 2) The complement protein cascade is the same for the classical pathway, alternative pathway, and lectin pathway beginning with the activation of A) C1. B) C2. C) C3. D) C5. E) C6. 3) Which of the following does NOT increase blood vessel permeability? A) Kinins B) Prostaglandins C) Lysozymes D) Histamine E) Leukotrienes 4) Which of the following does NOT provide protection from phagocytic digestion? A) Preventing formation of phagolysosomes B) Killing white blood cells C) Causing formation of phagolysosomes D) Ability to grow at a low pH E) Biofilms

Found in phagocytes and epithelial cells Small (< 100 amino acids) Cationic positive net charge at physiological pH Arginine and/or lysine rich Amphiphilic: also hydrophobic domains Microbial killing through membrane permeabilization and other mechanisms Example: defensins

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 Host derived proteins  Transferrin: blood and tissue fluid  Lactoferrin: milk, saliva, mucus  Bind iron which is essential to microbe  Microbes counteract with siderophores or iron binding protein receptors 35

 Relatively uniform response to a variety of causes  Infection  Physical agents like heat, radiation etc  Chemical agents like acids, bases etc.  Key signs are rubor (redness), dolor (pain), calor (heat), and tumor (swelling)  Local response includes vasodilation and increase of permeability, phagocyte migration and phagocytosis, tissue repair  Systemic response mediated by TNF  and acute phase proteins like C-reactive protein up to 1000x fold increased) can lead to fever, shock, disseminated coagulation 36

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 Innate immunity is widely conserved, functional upon birth, operates via pattern recognition and TLR, has no memory  Key cells in innate immunity are epithelial cells and phagocytes  Phagocytosis is enhanced by opsonins  Phagocytes kill via oxygen radicals, antimicrobial peptides, low pH, and enzymes.  The effector molecules of innate immunity are complement (killing, inflammation, enhanced phagodytosis), antimicrobial peptides (killing), interferons (activation of host antiviral defenses), and iron binding proteins (deprive microbes of iron). 38

Prerequisites: One of the following; MICR 201+MICR 202, MICR 300, BIOL 380, or instructor consent. Questions? /call Dr. Edith Porter at (323) or drop by at ASCL First line defense from concept to molecules Emphasis on primary research and hands on training in current methods in innate immunology including flow cytometry Lec: MW 9: :40 am * Lab: M 10:50 – 2:20 pm * Rec: W 10:50 – 11:40 am