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The Immune System
AtifHassanKhirelsied,B.Sc.,M.Sc.,Ph.D.
Departmento B oc em stry
Faculty
of
MedicineUniversityofKordofan
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mmun ymmun y
Immune(Latin
immunus)
=to
be
free,
exempt
mmun ycan ena ura oracqu re
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Theimmune
system:
e mmunesys em sacomp exne wor o
againstinvadingpathogensandtheirtoxins
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Thepathogens
= seasecaus ngm croorgan sms
bacteria
fungi,
pro ozoa,
parasite,
prion
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eant gen
Antigenswereoriginallydefinedasnonselfmolecules
.
Inpractice,thetermantigenisusedtomeanany
moleculerecognizedbytheimmunesystem.
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eant gen
Antigenswhichinduceadaptiveimmunityarecalled
immunogens.
Allimmunogensareantigens,butsomeantigensarenot
necessarilyimmunogens
and
are
known
as
hapten.
Haptens,arenotimmunogenicunlesstheyarecovalently
linkedto
immunogenic
carriers
called
adjuvant
(usually
proteins).
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Thehapten
Asubstance
that
is
non
immunogenic
but
which
can
react
withtheproductsofaspecificimmuneresponse.Haptens
responsewhenadministeredbythemselvesbutwhichcan
whencoupledtoacarriermolecule.
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Theepitope
and
paratope of
an
antibody
A. EpitopeorAntigenicDeterminant
Thatportionofanantigenthatcombineswiththeproductsof
aspecificimmuneresponse.
. ara ope s ecomp emen arypar o ean o y a
recognizesthe
epitope
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Thepathogens
Invadingmicroorganismsenterthebodiesthrough
di erentroutesand avedi erent a itatsint e
Theorgansoftheimmunesystemarestrategically
positionedthroughoutthebody.
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immunesystem
.
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Levels of
Figure 17.7
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Theimmune
system:
Innateimmunityispresentcontinuously,itisa
e ensemec an sm a spresen rom r .
Acquiredimmunityisinducedbythepresenceof
foreignmaterialandisusuallyquitespecific
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Innate Adaptive
Non-specific Immunity Specific Immunity
Antigen-independent Antigen-dependent
Immediate response Delayed response
Not antigen-specific Antigen-specific
No immunologic memory Immunologic memory
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Thebodydefenselines
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Theelementsoftheinnate(natural)immune
systeminclude;
Anatomicalbarriers.
Secretorymolecules.
Cellularcom onents.
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NaturalresistanceisthefirstNaturalresistanceisthefirstlinesofdefencelinesofdefence
TearsSalivaant acter a
enzymesantibacterial
enzymes
SSkin preventsMucus liningstraps
dirtandmicrobesen ry
Stomachacid
lowpH
kills
goodgut
harmfulmicrobes competebad
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Thenaturalresistance
Ph sicochemicalbarrierstoinfections
System/Organ Active
component Effector
Mechanism
Skin Squamous cells; Desquamation;flushing,
GItract Columnarcells Peristalsis,lowpH,bileacid,,
Lung Trachealcilia Mucocialiary surface
Nasopharynx
ande e
Mucus,saliva,tears Flushing,lysozyme
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Thenaturalresistance
System/Organ Active EffectorMechanism
Circulationand
l m hoidor ans
Phagocytic
cells
Phagocytosis and
intracellularkillin
NKcellsand Directandantibody
LAK dependentcytolysis
IL2activatedcytolysis
LAK:lymphokine activatedkillercells
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Thenaturalresistance
Humoralinnatebarrierstoinfections
System/
Organ
Activecomponent EffectorMechanism
Serum Lactoferrinand
Transferrin
Ironbinding
Interferons Antiviralproteins
TNFalpha antiviral,phagocyteactivation
Lysozyme Peptidoglycanhydrolysis
Fibronectin Opsonizationand
phagocytosis
Complement Opsonization,enhanced
phagocytosis,inflammation
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Theinflammation
therecruitmentofphagocytic cells.
Humoralfactorsintheserumorformedatthesiteof
n ec onp ay
an
mpor an
ro e
n
n amma on.
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Thecomplement
system
Isacomplementtoantibodymediatedimmunity.
Consistsofthirtyfiveinteractingplasmaand
membraneassociated
proteins
which
contribute
to
.
Itisthemajorhumoralnonspecificdefense
mec an sm.
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Thecomplement
system
Onceactivatedcomplementcanleadtoincreased
vascular
permeability,
recruitment
of
phagocytic cells,
and l sis and o sonization of anti ens.
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Thecomplement
system
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Thecoagulation
system
contributetothenonspecificdefensesbecauseof
theirability
to
increase
vascular
permeability and
actasc emotact c agents orp agocyt c ce s.
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Thecoagulation
system
antimicrobial.Forexample,betalysin,aprotein
producedby
platelets
during
coagulation
can
lyse
manyGrampositivebacteriabyactingasacationic
.
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Thecellularcomponentsoftheinnate
mmun ty nc u e;
1. Phagocytes (monocytes,macrophages)
2. PMNCs(neutophils,
eosinophils,
basophils).
3. Natural
killer (NK)
cells.
. .
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Partoftheinflammatoryresponseistherecruitment
o neutrop i s andmacrop ages tositeso
Thesecellsarethemainlineofdefenseinthenon
specificimmunesystem.
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.
PMNsrecruitedtothesiteofinfection
p agocy ose nva ngorgan smsan em
intracellularl .
PMNscontributetocollateraltissuedamagethat
occursduringinflammation.
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unc on np agocy os s an n race u ar ngo
microorganisms.
Actas
antigen
presenting
cells,
induce
adaptive
responses.
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Naturalkiller(NK)cellsarelymphocytesthatcan
recognizeand
destroy
viral
or
cancerous
cells.
.
tobe
abnormal
(i.e.
virally
infected
or
cancerous)
causetheabnormalcelltoundergoapoptosis.
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Phagocytosis
M h
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Macrophages.
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Oxygendependentmechanismsofintracellular
killing
Reaction Enzyme
H2O2 + Cl- --> OCl- + H2O
Myeloperoxidase
- + 2 --> 2 +- + 2
+ -- - 2 2 2 2
H O --> H O + O Catalase
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Oxygenindependentmechanismsofintracellular
ng
ec or o ecu e unc on
Cationic
roteins
includin
Dama eto
microbial
membranes
cathepsin)
Lysozyme Splitsmucopeptide inbacterialcell
wall
Proteolyticand
hydrolytic
iron
Digestionof
killed
organisms
enzymes
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systeminclude:
Recognitionandremovalofantigens.
Activationofthecomplementsystem.
Recruitmentofimmunecellstositesofinfectionandinflammation..
Inductionoftheadaptivesystemwhennecessary.
Comparison between innate and adaptive immunity
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Comparison between innate and adaptive immunity.
Attribute Innate Immunit Ada tive Immunit
Response time Minutes/hours Days
Specificity Specific for molecules and
molecular patterns
Highly specific, discriminate minor
differences in molecular structures
Diversity A limited number of germline
encoded receptors
Highly diverse, very large number
of receptors arising by genetic
recom na on
Memory responses None Persistent memory
Self/nonself
discrimination
Perfect, no microbe specific
patterns in host
Very good, occasional failure of
discrimination
Soluble components Many antimicrobial peptides and
proteins
Antibodies
,
macrophages, neutrophils) NK
cells, dendritic cells
, ,
cells