Immuno3 &4 Q Innate Immunity & Complement

8/7/2019 Immuno3 &4 Q Innate Immunity & Complement

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LECOM-Pharmacy School

Immunology 3 & 4

Dr. Saber Hussein

Innate Immunity & Complement



O bjectives

1. The early defense against infections and cancer 2. Recognition of microbes by the innate immune system

3. Components of innate immunity

± Physical and chemical barriers (e.g. epithelial barrier, stomach

acidity) ± Phagocytes: neutrophils and monocytes/macrophages

± Natural killer cells

± The complement system

± Cytokines of innate immunity

± Other plasma proteins of innate immunity

4. Microbes evasion of the innate immunity

5. How does innate immunity stimulate the acquired

immunity?



Innate Immunity

Natural, none-adaptive

Nonspecific to an antigen but recognize and fight

microbes

Phagocytes: Monocytes, macrophages, PMNneutrophils

Natural killer (NK) cells

Complement system

Exterior defenses: Skin, Stomach acidity, Mucus,

Cilia, Microflora, Lysozyme in tears, Flushing of

urinary tract



Cytokines of Innate Immunity

Cytokines are small soluble proteins produced by many cells such as

macrophages

They mediate immune and inflammatoryreactions

They are the tool of communication among

leukocytes and between those and other cells



Cytokines produced by macrophages

Tumor necrosis factor (TNF)

Interleukins (IL):

± IL-1

± IL12 ± IL-10

± IL-6

± IL-15

± IL-18

Type I interferons:

± IFN-E

± IFN- F



Cytokines of Innate ImmunityCytoki e ri cipal cell

so rce

ri cipal cell lar targets

iologic effect

T acrophage, T cell ndothelial cell: activation

eutrophil: activation

ypothalamus: fever

any cell types: apoptosis

I -1 acrophage,endothelial cell,

epithelial cell

ndothelial cells: activation

I -12 acrophages

endritic cellscells T cells: I -K

synthesis, increased cytolytic

activityI -K cells, T cells Activation o macrophages

Type I

I sI -E acrophages

I - F ibroblasts

All cells: antiviral activity,

increased I expression

cells: activation



Innate Immunity

Natural, none-adaptive, Nonspecific

Phagocytes: Monocytes,macrophages, PMNneutrophils

Natural killer (NK) cells

Complement system

Exterior defenses: Skin,

Stomach acidity, Mucus,Cilia, Microflora,Lysozyme in tears,Flushing of urinary tract

Physical Barriers



Functions of activated macrophages Macrophages may be

activated by signals from

many surface receptors.

± Receptor for bacterial

endotoxin (LPS), which

transduces signals via an

attached Toll-likereceptor

± Receptor for the most

important macrophage-

activating cytokine, IFNK

Signals from activating receptors stimulate the production of several proteins, which

mediate the important functions of macrophages.

Different M* surface receptors may stimulate distinct or overlapping responses

Common feature is that they stimulate the production of transcription factors, which

result in the production of various proteins



Functions of Natural killer (NK) cells

NK cells kill host cellsinfected by intracellular

microbes

± eliminating reservoirs of

infection. NK cells secrete IFNK in

response to IL-12

produced by macrophages

IFNK activates the

macrophages to kill

phagocytosed microbes



Reticuloendothelial system & Normal flora

Reticuloendothelial system & Competition by Normal flora

Normal flora on

Oral cavitySkin



Soluble Factors &

Physiological responses Soluble Factors:

1. Lysozyme

2. Complement

3. ntiproteinases

4. C-reactive protein

5. DN se6. RNases

Physiological responses:

± Chemotactic factors from

infecting agents

Bacteria F-Met

peptides

Injured tissue

± Mast cells & PMN

± Leukotrienes &

± Histamines



Mechanisms of

killing

Toxic oxygen

± Oxygen radicals

± Hydrogen peroxide

± Hypochlorous acid(HOCl)



Innate & adaptive immunityInnate Immunity

Pathogen recognized by receptors

encoded in the germline Receptors have broad specificity,

i.e., recognize many relatedmolecular structures called P MPs(pathogen-associated molecular

patterns) P MPs are essentialpolysaccharides &polynucleotides that differ littlefrom one pathogen to another butare not found in the host (mannose)

Receptors are PRRs (patternrecognition receptors)

Immediate response

No memory of prior exposure

Occurs in all metazoans?

Adaptive Immunity

Pathogen recognized byreceptors generated randomly

Receptors have very narrowspecificity; i.e., recognize a

particular epitope

Most epitopes are derived from

polypeptides (proteins) andreflect the individuality of the

pathogen

Receptors are B-cell (BCR ) andT-cell (TCR ) receptors for

antigen Slow (3 -5 days) response(because of the need for clonesof responding cells to develop)

Memory of prior exposure

O

ccurs in vertebrates only



Innate

&daptive

Immunity



C-Reactive

Protein

CRP belongs to the pentaraxin

family of proteins

± so-called because it has five identical

subunits, encoded by a single gene on

chromosome 1, which associate to form a

stable disc-like pentameric structure

It reacts with the somatic Cpolysaccharide of St rept ococcus

pneumoniae

In the presence of calcium, CRP

specifically binds to phosphocholine

moieties

± phosphocholine is found in phospholipid

membranes of many organisms

Pentameric structure

of CRP



CRP role in innate immunity

Binding phosphocholine gives CRP a host-defensive

role because:

± Phosphocholine is found in microbial polysaccharides

CRP-binding activates the classicalcomplement pathway

Opsonizes ligands for phagocytosis

± It neutralizes the pro-inflammatory platelet-activating

factor (PAF)

± It down-regulates polymorphs (neutrophil, eosinophil,

basophil)



CRP made in the liver CRP is exclusively made in the liver

Secreted in increased amounts within 6 hours of an

acute inflammatory stimulus (e.g. infection)

The plasma level can double at least every 8 hours,

reaching a peak after about 50 hours fter effective treatment or removal of the inflammatory

stimulus, levels can fall almost as rapidly as the 5-7-

hour plasma half-life of labeled exogenous CRP

The only condition that interferes with the "normal"CRP response is severe hepatocellular impairment



Defensins

Definition: ± family of abundant, modestly potent

cationic proteins that is found

in the primary granules of neutrophils and

in the lysosomes of some mononuclear phagocytes

Bactericidal

± can kill fungi and viruses too

One defensin is chemotactic for monocytes

± Neutrophils help to attract the "second wave" of leukocytes-

Mononuclear phagocytes



Defensins

ll of the following are protected by defensins

1. our epithelial surfaces

2. skin

3. lining of the GI tract

4. lining of the genitourinary tracts

5. lining of the nasal passages and lungs



Leukocytes extravasation

Blood vessel

Infected tissue



Complement

Alternative Pathway

Classic Pathway



O bjectives

1. Define complement

2. ctivation of the classical pathway

3. ctivation of the lectin pathway

4. ctivation of the alternative pathway

5. Describe the three functions of complement in

body defense

6. Complement deficiencies and disease



The complement system: (Chapter 2)

The enzymatic cascade ctivation of the complement cascade

1. The alternative pathway

2. The classical pathway

3. The lectin pathway

naphylactic and chemotactic products of thecomplement system

Membrane attack complex

Evasion of innate immunity by microbes

Role of innate immunity in stimulating adaptiveimmune responses



What is Complement?

Non-immunoglobulin serum proteins

Involved in:

i. Control of inflammation

ii. Stimulation of phagocytosis

iii. ctivation of cell lysis



O psonization (³Eat Me´ tag) & phagocytosis Preparation for eating

Phagocytosis facilitating process

O psonins are deposited on the g (bacteria or virus infected cell)

Important opsonins can label bacteria:

IgG

Complement fragments (e.g. C3b)



Sites of synthesis Hepatocytes

Macrophages, various tissues

Epithelial cells, GI tract

Monocytes, in blood



Functions of complement Direct killing of bacteria & virus-infected

cells by lysis mediated by MAC

I ndirect killing by opsonization followed

by phagocytosis & intracellular killing

Immunization does NOT increase

complement concentration in the serum



Role of C3 in bacterial

clearance and killing

1. C3 bound to bacteria as C3b or iC3b binds to CR1 onerythrocytes, which transport

bacteria through circulation

2. C3 acts as focus for the

deposition of lytic M C on bacterial cell membrane

3. It ligates complement receptor on phagocytes

4. Complement, in turn, activates

the phagocyte leading to Bacterial phagocytosis,

Respiratory burstgeneration and

Bacterial killing

intermediate



Activators of the alternative

pathway (AP) Lipopolysaccharides (LPS)

Bacterial cell walls

Cell walls of yeasts

Aggregated IgA

Cobra venom NO need for A b-Ag complex or IgM for

activation



Activation cascade

of the

Alternative

Pathway

C3b binds foreign substance

C3b + Serum¶s Factor B C3bB

Factor D cleaves Factor B C3bBb C3bBb acts as C3 convertase:

C3 C3a + C3b

± Properdin regulates the process; stabilizes C3bBb.

± Factor I & H inactivate free C3b

AlternativePathway



Activation of Classical Pathway (CP)

CP is activated by: ± Antigen-IgG complex

± Pentameric IgM

Non-activators of CP: ± IgG4

± IgA

± IgE

± They lack C1q

receptors they

cannot bind C1q

Classical pathway



Steps of CP activation

Step 1:A

ctivation of C1 ± C1q-FcIgG activates C1r &C1s

± C1s activates C4 C4a +C4b

Step 2: Activation of C4

± C4 C4a + C4b Step 3: Activation of C2 by

C4b ± C4b + C2 C4b2a (C3-

convertase) + 2b

Step 4: Activation of C3

Step 5: Activation of C5,C6 & C7

Step 6: Activation of C8 &C9

Classical pathway



Complement

Classic Pathway

Alternative

Pathway

Common Pathway



MAC & Cell Lysis



Split Products and Their Activity

Activities of complement fragments



The Lectin Pathway (LP)

Activator: Mannose-binding lectin (MBL), a plasma protein that is similar to C1q

MBL binds to terminal mannose (sugar) on the

surface glycoprotein of microbes This lectin activates the classical pathway

proteins

Difference between LP and CP: ± LP activation does not require antibodies

Therefore, LP activation is part of the innate immune

system



Three functions of complement in host defense

1. Opsonization:

± C3b binds to microbes and so enables the phagocytes to grab the microbe, via their C3breceptor, and phagocytose it

2. Chemotactic activity of C5a:

± This complement fragment attracts neutrophilsand monocytes to the site of infection

± C5a promotes inflammation at the site of complement activation

3. Formation of membrane attack complex(MAC)

± MAC forms a pore (hole)in the membrane of themicrobe leading to the loss of cellular contents, lysis

of the microbe and death of the microbe



Complement Proteins¶

Deficiencies Alternative pathway defects Susceptibility

to H aemophilus influenzae

Defects of F act or D & P roperdin increase

N eisseria infection

C5 deficiency, less severe consequences,

but increases susceptibility to N eisseria gonorrheae & N. meningitidis

l



Complement &

disease pathogenesis

Complement may cause disease pathogenesis by:

1. Systemic production of anaphylaxis such as after Gram-negative sepsis

2. Insertion of MAC into hostcell membrane leading tocellular activation andstimulation of membranearachidonic acid metabolism

3. Fixation of C3b to immunecomplexes located in tissuescausing recruitment andactivation of tissue andcirculatingWBCs



Heritable angioedema (HA

E) C1-inhibitor deficiency

Autosomal dominant trait inheritance

Edema in various organs & tissues

Especially bad:

± Edema of intestine and throat

Treatment

± Epinephrine for emergency treatment



A

cquired angioedema Caused by an autoantibody to C1 inhibitor,

This leads to inactivation of C1 inhibitor

± A result similar to HAE:

C1 inhibi t or becomes deficient

Documents

Immuno3 &4 Q Innate Immunity & Complement