Section 11: Section 11:

Extracellular MacromoleculesExtracellular Macromolecules

3. Innate immunity3. Innate immunity& inflammation& inflammation

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The immune systemThe immune systemThe immune systemThe immune systemmain function:main function:

distinguish foreign/abnormal molecules & cellsdistinguish foreign/abnormal molecules & cells from one's own molecules & cellsfrom one's own molecules & cells

destroy/neutralize the foreign/abnormal onesdestroy/neutralize the foreign/abnormal onestwo major divisions: innate & adaptivetwo major divisions: innate & adaptiveinnate immune response overviewinnate immune response overview

relatively rapid & nonspecificrelatively rapid & nonspecificmicroorganisms encounter macrophagesmicroorganisms encounter macrophagesinteraction activates macrophagesinteraction activates macrophagesmacrophages secrete signal factors which triggermacrophages secrete signal factors which trigger

•inflammationinflammation•leukocyte activationleukocyte activation•phagocytosisphagocytosis•activation of lymphocytesactivation of lymphocytes (adaptive immune response) (adaptive immune response)1

DefinitionsDefinitionscytokines:cytokines: proteins that are intercell signal factors; if the cells are proteins that are intercell signal factors; if the cells are

leukocytes, the term interleukins (IL) is sometimes used,leukocytes, the term interleukins (IL) is sometimes used,especially in naming cytokines, especially in naming cytokines, e.ge.g., IL1, IL2, etc.., IL1, IL2, etc.

chemokines: chemokines: small chemoattractant cytokines that stimulate the small chemoattractant cytokines that stimulate the migration and activation of cells, especially phagocytic cells and migration and activation of cells, especially phagocytic cells and lymphocyteslymphocytes

chemotaxins:chemotaxins: substances that attract leukocytes substances that attract leukocytesThe early phases of the host response to infection depend on The early phases of the host response to infection depend on innate innate

immunityimmunity in which a variety of innate resistance mechanisms in which a variety of innate resistance mechanisms recognize and respond to the presence of a pathogen. Innate immunity recognize and respond to the presence of a pathogen. Innate immunity is present in all individuals at all times, does not increase with repeated is present in all individuals at all times, does not increase with repeated exposure to a given pathogen, and discriminates between a group of exposure to a given pathogen, and discriminates between a group of related pathogens. (from related pathogens. (from ImmunobiologyImmunobiology 5 ed. Janeway et al. 2002) 5 ed. Janeway et al. 2002)

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Definitions Definitions (cont’d)(cont’d)InflammationInflammation is a general term for the local accumulation of is a general term for the local accumulation of

fluid, plasma proteins, and white blood cells that is initiated fluid, plasma proteins, and white blood cells that is initiated by physical injury, infection, or a local immune response. by physical injury, infection, or a local immune response. This is also known as an This is also known as an inflammatory responseinflammatory response. Acute . Acute inflammation is the term used to describe early and often inflammation is the term used to describe early and often transient episodes, whereas chronic inflammation occurs transient episodes, whereas chronic inflammation occurs when the infection persists or during autoimmune diseases. when the infection persists or during autoimmune diseases. Many different forms of inflammation are seen in different Many different forms of inflammation are seen in different diseases. The cells that invade tissues undergoing diseases. The cells that invade tissues undergoing inflammatory responses are often called inflammatory responses are often called inflammatory cellsinflammatory cells or an or an inflammatory infiltrateinflammatory infiltrate..

(from (from ImmunobiologyImmunobiology 5 ed. Janeway et al. 2002) 5 ed. Janeway et al. 2002)

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Macrophage activationMacrophage activationmacrophages havemacrophages havenumerous receptors for numerous receptors for molecules on bacterial molecules on bacterial surfacesurface

important example: LPSimportant example: LPSbinding to LPS receptorbinding to LPS receptor

activates intracellular activates intracellular messengersmessengers

transcription of several transcription of several target genestarget genes

result:result:release of lipid mediatorsrelease of lipid mediators**secretion of cytokines,secretion of cytokines,** including chemokines including chemokines

4 *macrophage effectors

Bacterial components: endotoxinsBacterial components: endotoxins lipopolysaccharides (LPS) lipopolysaccharides (LPS)

akaaka endotoxins endotoxins ( (structure at rightstructure at right))

part of the outer membrane of part of the outer membrane of gram–negative bacteriagram–negative bacteria

lipid part called lipid part called lipid Alipid A::6 hydrocarbon chains6 hydrocarbon chains

effectseffects• activate phagocytesactivate phagocytes• leukocyte–toxicleukocyte–toxic• antigenicantigenic• cause release of cause release of

lytic enzymes lytic enzymes from leukocytesfrom leukocytes

O

O

OO

O

OH

O

OHO

NH

OO

OOO

O NH

O

O

OPO P

OOO

OOH

O

core O-antigen–

––

– l i p i d

A

core: 8-10 glycosidic units O-antigen: 0-40 glycosidic units5

Surface structures of Surface structures of gram negative bacteriagram negative bacteria

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Macrophage effectors draw plasma proteins, Macrophage effectors draw plasma proteins, leukocytes: inflammationleukocytes: inflammation

lipid mediators released by lipid mediators released by macrophages (prostaglandins, macrophages (prostaglandins, leukotrienes, PAF, etc.) produce leukotrienes, PAF, etc.) produce the inflammatory responsethe inflammatory responsevasodilation (vasodilation (redness, heatredness, heat))increased spacing between capillary increased spacing between capillary endothelial cells endothelial cells

this causes plasma proteins* to diffuse this causes plasma proteins* to diffuse into interstitium, changing osmotic balance into interstitium, changing osmotic balance

result:result: net fluid flow into interstitium net fluid flow into interstitium ((swellingswelling))

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prostaglandins, etc.

cytokines

chemokines

protein

fluid

** including including complement proteins (complement proteins (slide 11slide 11))

Osmotic balanceOsmotic balance

capillarycapillary interstitialinterstitial

lumenlumen spacespace

PP hydrostatichydrostatic oncoticoncotic

pressurepressure pressurepressure

(blood pressure) (blood pressure) (plasma-colloid (plasma-colloid osmotic pressure) osmotic pressure)

sourcesource: plasma proteins: plasma proteins

60-80 g/L ~ 1-1.3mM60-80 g/L ~ 1-1.3mM

for further details, see Sherwood, p. 3658

Macrophage effectors draw leukocytes: Macrophage effectors draw leukocytes: inflammationinflammation

cytokines activate capillary cytokines activate capillary endothelial cells via TNF- endothelial cells via TNF-

effects of activation:effects of activation: proteins expressed on luminal proteins expressed on luminal surface of endothelial cells surface of endothelial cells

SelectinsSelectins bind to specific surface glyco bind to specific surface glyco moieties on leukocytes moieties on leukocytes

ICAMsICAMs bind to bind to integrinsintegrins on leukocytes on leukocytes

result: neutrophils,monocytes extra-result: neutrophils,monocytes extra- vasate (enter interstitium) ( vasate (enter interstitium) (slide 13slide 13))

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cytokines: TNF-

leukocyteextravasation

Macrophage cytokines’ Macrophage cytokines’ systemic inflammatory effectssystemic inflammatory effects

cytokines (TNF-cytokines (TNF-, IL-1, IL6), IL-1, IL6) mobilize neutrophils (bone marrow)mobilize neutrophils (bone marrow) endogenous pyrogens (hypothalamus)endogenous pyrogens (hypothalamus) activate activate acute-phase responseacute-phase response (liver) (liver)

acute-phase proteinsacute-phase proteins secreted into blood by hepatocytessecreted into blood by hepatocytes

e.g., e.g., mannose-binding (MB) lectinmannose-binding (MB) lectinC-reactive protein C-reactive protein ((CRPCRP)*)*

main effects:main effects:•opsonize (bind to & mark for phagocytosis)opsonize (bind to & mark for phagocytosis) bacteria for leukocytes bacteria for leukocytes

•activate complement cascadeactivate complement cascade10

CRP

*clinically useful marker for disorders, e.g., CVD

Complement activation & effectsComplement activation & effectsthe the complementcomplement system is a set of plasma proteins that act system is a set of plasma proteins that act

together to attack extracellular forms of pathogenstogether to attack extracellular forms of pathogensthey get to infection site via permeable endotheliumthey get to infection site via permeable endotheliumactivationactivation: via a series of proteolytic steps: via a series of proteolytic steps

(a cascade like blood clotting)(a cascade like blood clotting)

MB= mannose-binding11

C3b

MB lectin

Complement effectsComplement effectscomplement activation leads to activation of mast cellscomplement activation leads to activation of mast cells

(by C3a, C5a)(by C3a, C5a)mast cells secrete histamine, a vasodilatormast cells secrete histamine, a vasodilator

C5b-C9 form pore in bacterial membrane, causing leakage & lysis (C5b-C9 form pore in bacterial membrane, causing leakage & lysis (seesee S11L4 S11L4slsl23)23)opsonization: marking microorgan-opsonization: marking microorgan-

ism’s surface for phagocytesism’s surface for phagocytes(C3b, C4b)(C3b, C4b)opsoninsopsonins bind to bacteria & bind to bacteria &then bind to a surface receptorthen bind to a surface receptoron a phagocyteon a phagocyte

recruitment of leukocytesrecruitment of leukocytessome components aresome components arechemokineschemokines

12CR1

C3b

Leukocyte adhesion & extravasationLeukocyte adhesion & extravasation

Lodich et al., 5 ed. Fig. 6-3013

Phagocytosis & pathogen destructionPhagocytosis & pathogen destructionbacteriocidal reactions in phagolysosomesbacteriocidal reactions in phagolysosomes

2 O2 O22 + NADPH + NADPH →→ NADPH NADPH++ + O + O22–– NADPH oxidaseNADPH oxidase2 O2 O22–– + 2 H + 2 H++ → → OO22 + H+ H22OO22 superoxide superoxide dismutasedismutase2 Cl2 Cl–– + 2 H + 2 H22OO22 → → 2 ClO2 ClO–– + 2 H + 2 H22OO myeloperoxidasemyeloperoxidase

other lysosomal bacteriocidesother lysosomal bacteriocideslysozymelysozyme lyses glycopeptide coatlyses glycopeptide coatproteasesproteases hydrolyze proteinshydrolyze proteinsdefensinsdefensins cationic peptidescationic peptides

disrupt cell membranedisrupt cell membraneif/when any of the above lyticif/when any of the above lyticmolecules escape phagocytes,molecules escape phagocytes,damage to local tissues resultsdamage to local tissues resultspart of part of chronic inflammationchronic inflammation14

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4. The Adaptive (Acquired)4. The Adaptive (Acquired)Immune SystemImmune System