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MICR 201 Microbiology for Health Related Sciences

Lecture 9: Innate ImmunityEdith Porter, M.D.

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Lecture outline 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

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Concept of immunity

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

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Overview of host defenses

First Line of Defense Second Line of Defense

• NK cells

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Physical (mechanical) defense of skin

Outer body surface

Keratin barrier

Epithelial cell shedding

Dryness

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Physical (mechanical) defense of mucosa

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

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Chemical defense

Sebum, unsaturated fatty acids

“antimicrobial lipids”

Low pH Skin (pH 3-5)

Stomach (pH 1.5 – 3)

Vagina (pH 3 – 5)

Urine (pH 6)

http://www.niams.nih.gov/Health_Info/Acne/images/normal.jpg

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Normal microbiota as part of host defense

Competes with potential pathogens for nutrients

Directly inhibits potential pathogens Lactobacilli: lactic acid, low pH Bacteriocins

Skin Tongue Esophagus

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Cellular elements of host defense

Epithelial Cells

Leukocytes

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Epithelial cells

Keratinizing in skin Non-keratinizing elsewhere

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Immune function of epithelial cells

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

Epithelial cell defense

TLR

Microbial Products(LPS, PG, etc)

Antimicrobial Peptides

Cytokines 12

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Leukocytes in peripheral blood

Granulocytes

Monocytes Lymphocytes

Natural Killer Cells

Anti-viralAnti-bacterial Anti-fungal

Anti-parasiticAnti-allergic

Anti-bacterial Anti-fungal

B-Ly : antibody production

T-Ly: orchestrate

Anti-parasiticAnti-allergic

neutrophil eosinophil basophil

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Leukocytes in tissue

Macrophagein bone marrow Dendritic cell

Mast cell

Anti-parasiticAllergic responses

Communicates with

lymphocytes

Clears bacteria and fungi in

tissues

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Origin of leukocytes

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

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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

Phagocytosis

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Phagocytes in Action

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Key steps of opsonophagocytosis (1)

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Key steps of opsonophagocytosis (2)

Chemotaxis Opsonization Adherence (attachment) Ingestion (engulfment)

Pseudopods Phagosome

Phagolysosome Killing and digestion

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Chemotaxis

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”)

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Opsonization

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

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Killing and digestion by phagocytes

Oxygen dependent Oxidative Burst Reactive oxygen and reactive nitrogen

intermediates Oxygen-independent

Antimicrobial peptides Low pH Enzymes (Hydrolases, proteases,

phopholipases)

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Effector molecules of host defense

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

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Complement system

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

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The Complement Cascade

Early events: proteolytic cascade generates bioactive cleavage fragments

C1 C4 C2 C3 C5 C6 C7 C8C9n

Late events: Protein polymerization generate a pore on target cell

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Activation of complement system

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

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Outcomes of Complement Activation

Always the samePore formation on microbe and direct

killing (C5b- C9n)Opsonization and improved

phagocytosis (C3b) Inflammation and recruitment of

phagocytes (C5a, C3a, C4a)

29Figure 16.9 (3 of 5)

Complement mediated enhancement of phagocytosis

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Pro-inflammatory action of complement

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

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Microbial killing by complement C5b-C9n

1) Innate immunity isA) 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 ofA) C1.B) C2.C) C3.D) C5.E) C6.

3) Which of the following does NOT increase blood vessel permeability?A) KininsB) ProstaglandinsC) LysozymesD) HistamineE) Leukotrienes

4) Which of the following does NOT provide protection from phagocytic digestion?A) Preventing formation of phagolysosomesB) Killing white blood cellsC) Causing formation of phagolysosomesD) Ability to grow at a low pHE) Biofilms

Practice questions

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Antimicrobial peptides

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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Interferons (IFN a and IFN )b : act on host cells to increase production of antiviral proteins

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Iron binding proteins

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

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Acute inflammation

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 TNFa and acute phase proteins like C-reactive protein up to 1000x fold increased) can lead to fever, shock, disseminated coagulation

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Process of acuteinflammation

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Important to remember

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).

W2011 MICR 450 Innate Immunity (4)

Prerequisites: One of the following; MICR 201+MICR 202, MICR 300, BIOL 380, or instructor consent. Questions? email/call Dr. Edith Porter at eporter@calstatela.edu , (323) 343 6353 or drop by at ASCL 355

First line defense from concept to moleculesEmphasis on primary research and hands on training in current

methods in innate immunology including flow cytometry

Lec: MW 9:50 - 10:40 am * Lab: M 10:50 – 2:20 pm * Rec: W 10:50 – 11:40 am