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BasicconceptsofImmunology
Immunology-is definedastheunderstandingofbody defensemechanismsItgrewwithincreasing
understandingofmicroorganisms.It becameaninteresttoknow howthebodydefendsitself against
infections.EdwardJennershowedthatthebodycouldrespondtoforeignsubstances andgeneratethe
abilitytodefenditselfinsubsequentinfections
Immunity-isthenaturaldefensethatallowonetoavoidorfightoffdiseases,infectionorothertypesof
biologicalinvasionofthebody
Evolutionaryimmunologytrend
- Isthestudyoftheevolutionof immunityandtheimmunesystemoverages.Itincludes the
studyofphysicaland historical developmentoftheability to recognizeforeignantigenic
material. The trend can be either directional changes within a single lineage or parallel
changeacross lineagesinotherwordsseverallineagesundergoingthesamesortofchanges
howevernotjustany changecountsas atrend.
Principlesonimmunology
Theenvironmentiscontaminatedwithforeignagents,someofwhichareinfectiousagents. Therefore
thebodyneedsa systemtoresistentry,multiplicationandestablishmentofinfectiousdiseasesThis
systemiswhat isreferredtousimmune.
Branchesofimmunology
i. Immunopathology-Isassociatedwithimmunemediateddisorders
ii. Immunochemistry-involvesanalysisof thestructureandfunctionsof antibodiesand
complementproteins
iii. Immunohematology-involvesthestudyofbloodgroupantigensandbloodassociateddisorders
together
iv. Immunogenetics-involvesthestudyofsuchgenes
v. Transplantationimmunology-involvestheunderstandingofimmuneresponsesinthe
replacementof functionallydefectiveordiseased organs/tissuewith normal one
vi. Tumorimmunology-theroleofbodydefensemechanismsisstudiedagainsttransformedcellsor
thosewithabnormalgrowth
vii. Reproductiveimmunology-involvesstudyofall reproductivesystems
viii. Cancerimmunology-involves studyofalltypesofcancers
Classificationofimmuneresponses
Theimmunesystemin mancanbe broadlydivided intotwo:
1. Innate(non-specific)and
2. Acquiredadaptive(specific)immunity.
-Innatemechanismsprovidefirstline ofdefensewithoutmemory whileadaptiveresponsesare
characterizedbyrecognition,specificityandmemory.Whenthesemechanismsarebreachedby
infection or injury then specific immune responses are stimulated. The adaptive defense
mechanismsaredesignatedHumoralandcellularimmuneresponses.Humoralresponsesinvolve
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solublecomponentsincludingimmunoglobulin’s(antibodies)andcomplementsofthecellular
compartmentoftheimmunesystem.
Determinants ofinnateimmunity andcomponentsof adaptiveimmuneresponses areillustrated
FUNCTIONALIMMUNITTY ADAPTIVEIMMUNITY
INNATEIMMUNITY -Cellularimmuneresponses -Humoralresponses
-Physicalbarriers a)T cells Complementproteins&
Antibodies(Abs)
-Geneticfactors b)Macrophages
-Solublecomponents
-Cellularcomponents
Generalcharacteristicsofimmune systems
InnateImmunity
AcquiredImmunity
Providesfirstlinedefensewithentryagainst
invadingorganisms
Providesecondlinedefense
Isimmediatedevelopafterexposuretoinfectious
agents
Takestimetodevelopafter exposuretoinfectious
agent
Involvesanatomicalfeatures,cellularfactorsand
biochemicalsubstances
Mainlyinvolvescellular factors
Non-specificinnature
Isspecifictoagivenforeignagents(Antigens)
Thereisnoresistancetore-infectionthestrength
ofresponsein innateimmunitydoesnotincrease
withrepeatedexposureto adiseasecausing
organism(pathogen)
Confersresistancetore-infection-Thestrengthof
immunityincreasewithrepeatedexposuretoa
pathogen-demonstratesmemory
Donotrequireantigen-naturallyoccurring
Isanantigendepended-hastobestimulatedbyAg
Adaptiveimmunity
- Isaresponseto immunesystemchallenges.Itcan besubdividedinto2 passives:
✓
Active
✓
Passive
PassiveImmunity:IsgottenthroughbreastmilkcontainsAbs,ChemicalsorSubstancestailoredtooff
specificinvadesorfromcertain immunizationsTetanusantitoxins,whichcontainthe antibodyfromsome
otherpersonorfroman animal
Activeimmunity:ResultswhenthebodymakesAbsto apathogenbecauseit wasactuallyexposedto
thatpathogen.This can occurwhen onegetsan illnessand subsequentlybecomesimmuneor through
administrationofdeadorweakenedpathogensinavaccination
Generalcharacteristicsthat distinguishesbetween thespecificandnon-specific
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The2 systemsinterplaytherearecomponentsthatinfluenceadaptiveimmunity
Innateimmunemechanisms
• Duringprimaryexposuretoinfectiousagentsandtumors,non-specificmechanismsarevitalin
providingprotection.The determinantsofthisinnate immunityareinfluencedbyhost genetic
constitutional statusoftheindividual.Somedefense mechanismsarenotdirectly linkedtothe
immunesystemsuchasbarrierscreatedbytheskinandmucusmembrane,competitionfrom
normal bacterial flora in the gut, mucociliary clearance of pathogens and fungi statis
componentslikemetalchelators
Components ofinnateimmunity
1. Physical(Anatomical)barriers
a) Intactskin-Epithelialsurfacesofthe skinformaphysicalbarrierthatis impermeableto
mostinfectiousagents
- Skinactsasfirst linedefenseagainstthe invadingorganismsandtheirproducts
- The protectiveroleof theskinislostas soonasyouhavebrokentheskin
2. Mechanicalfactors
a) Hair,ciliaand theperistalticmovementhelps to cleardiseasesin the respiratoryand
gastrointestinalpathogen
b) Thetears andsaliva containchemicali.e. lysozymes–thatsplits open(lysis) ofwallsof
grampositivebacteria
c) Themucusinthe respiratorytractstrapandexpelinhaledmicro-organismsandnoxious
agentsthroughmucociliarysystem
3. Chemicalfactors(solublecomponents)
a) Thefattyacidsthatarepresentinsweatinhibitsgrowthof bacteria
b) Lysozyme present in saliva, tears, and nasal secretions causes lysis of cells of gram
positivebacteriac)-Defensin’sthatarefoundinthelungsand gastrointestinaltract
haveanti-microbialactivity
c) Acutephaseproteinsproducedbytheliverduringinfectionandconcentrationincrease
hundred folds. The poteins are progens which increases body temperature thereby
inhibitsthegrowthofmouthofd. c.organisms
d) Complement–agroupoftwentyor moreserumproteins thatarepresentin normal
serumaszymogensandonlyget activatedbypresenceof diseasecausingorganisms
uponactivationleadingto:
✓
Inflammation
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Lysis(splittingopen)ofcellwallofbacteria
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Chemotaxis(unidirectional)ofcellstothesiteofinfection
e) Lactoferrin:aresubstancesthatareonlyfoundinmilkoflactatingmotherstheybind
ironessentialnutrientfor growth.Theylimitthegrowthof bacteria
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f) Cytokines: chemical substances protein in nature
secreted by immune or non- immune cells;
interleukins, Interferon’s, Tumors Necrosis Factors
e.t.c.
4. Cellularcomponents
- Phagocytesandnaturalkillercells.Phagocyticcellsconsistof
mononuclearand polmorphonuclear(neutrophils)cellswhile
NK cells are large granular leukocytes. They eliminate
infectiousagents,tumorsand abnormalcells fromthebody
through non-specific mechanisms.In the CNC monocytes-
macrophagelineagecellsarethemajorcomponentsinvolved
inthe inflammatoryresponses.Phagocytesmediatethehost
defense through a process referred to as phagocytosis.
Infectious agents that adhere onto the phagocytes are
internalized and removed through a sequence of events
involving fusion of pathogen with lysosome ingestion and
hydrolysis of infectious agent by lysosomes and acid
hydrolases. Phagocytes are capable of producing
inflammatorycellmediatorssuchas interleukin-1(IL-1)and
tumornecrosisfactor(TNF)whichmediatetheactivationand
recruitmentofothercellstothe siteofinfectionor injury
Blood
Cells plasma
Erythrocytes leucocytes
Granulocytes(myeloid)
EosinophilisNeutrophilisBasophilisMonocytes,Mastcells Lymphnoidseries(A
granulocytes)
Blymphocytes T
lymphocytesNullcells
5. Geneticcomponents
- Non- specific immune responses are influenced by genetic
constitutionof the individual. Geneticfactorssuchasimmune
response genes are usually crucial elements in determining
susceptibilityor resistance and clinical expression of various
diseases. Certain genetic factors may confer resistance
against various infections. In malaria innate protection is
associatedwithnegativeDuffy(a,b)
6. Microbialantagonism
- Referstonon-pathogenicmicroorlivein thebody(urogenital,
digestive, respiratory (normal flora). They compete with
pathogenicmicrobesforsitesofcolonization,food– prevent
initialestablishmentmay produceantmicrobialcompounds
orinhibits growthof bacteria
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