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TheImmuneSystemandDisease
Chapter40
WhatisDisease?• Adiseaseisanychange,otherthaninjury,thatdisruptsthenormalfunctionofthebody.
• Whataremajoragentsofdiseaseotherthanenvironmentorgenetics?– Viruses,Bacteria,Protists,Fungi,andWorms.
• Howaretheyspread?– PhysicalContact,Contaminatedfoodandwater,infectedanimals
• Inthepast,peoplethoughtdiseasesweretheresultofcurses,evilspiritsornightvapors!
• Itwasuntilthe1850swhenLouisPasteurandRobertKochfoundthatdiseaseswerecausedbymicroorganismscalled“germs.”– TheirideaisnowcalledtheGermTheoryofDisease.
Howdowedefendagainstdisease?
• Welearnedearlierthereareantibiotics(bacteria)andvaccines(viruses)available.
• However,ourbodyhasitsownsetofdefenses,calledtheImmunesystem.
• Thefunctionoftheimmunesystemistofightinfectionthroughtheproductionofcellsthatinactivateforeignsubstancesorcells.Thisprocessiscalledimmunity.– Therearetwomajortypesofdefenses,nonspecificdefenseandspecificdefense.• Nonspecificislikethefortresswallstokeepstuffout!• Specificislikethesecurityguardsthattracksdownharmfulpathogensthathappentobreakinandgetthemout.
Koch’sPostulates• Seriesofrulesusedtoidentifythe
microorganismthatcausesaspecificdisease.(Stillusedtoday!)
• Theyareimportantbecauseidentifyingthepathogenthatcausesadiseaseinthefirststepinpreventingorcuringtheailmentsthattheyproduce.
1.Thepathogenshouldalwaysbefoundinthebodyofasickorganismandnotinahealthyone.
2.Thepathogenmustbeisolatedandgrowninthelaboratoryinpureculture.
3.Whentheculturedpathogensareplacedinanewhost,theyshouldcausethesamediseasethatinfectedtheoriginalhost.
4.Theinjectedpathogenshouldbeisolatedfromthesecondhost.Itshouldbeidenticaltotheoriginalpathogen.
Non-specificDefenses:FirstLineofDefense
• Skin,mucus,sweatandtears.• Mostimportant?SKIN!Manypathogens
cannotpenetratepasttheskin.– Note:Largestorganofthebody!
• Secretionsofthebody(mucus,salivaandtears)containlysozymeanenzymethatbreaksdownthecellwallsofmanybacteria.
• Oilandsweatglandsintheskinproduceanacidicenvironmentthatkillsmanybacteria.
• Pathogenscanalsoenteryourbodythroughyourmouthandnose,wheremucusandtrapsthemandciliapushpathogensawayfromyourlungs.
• Stomachacidanddigestiveenzymesdestroymanypathogensthatmaketheirwayintoyourstomach.
Non-specificDefenses:SecondLineofDefense
• Ifpathogensdomaketheirwaypastthisfirstlineofdefense,theybegintomultiplyquicklyandreleasetoxins.
• Thenthesecondlineofdefenseisactivated,theinflammatoryresponse.
• Theinflammatoryresponseisanonspecificdefensereactiontotissuedamagecausedbyinjuryorinfection.– Whitebloodcellsarereleased.– Bloodvesselsnearthewoundexpandtolet
theWBCshaveaccesstothepathogens.– Manyofthesearecalledphagocytesthat
engulfanddestroythepathogen.– Bodytemperaturerises,calledafever.This
helpsslowordestroythepathogen.– Heartrateincreasestopumpblood(WBCs)
faster.– Whenvirusesaredetected,cellsrelease
interferon,proteinsthatblockthesynthesisofviralproteinsandbuysthebodytimetorespondtotheattack.
SpecificDefenses
• Ifapathogenisabletogetpastthesetypesofnon-specificdefenses,thebodybeingsafullimmuneresponseusingspecificdefenses.
• Asubstancethattriggersthisiscalledanantigen.
• Therearetwotypesofcellsreleasedfortwoseparateactivities:– BLympocytes(Bcells)–HumoralImmunity
– TLympocytes(Tcells)–Cell-mediatedImmunity
SpecificDefense:HumoralImmunity• Whenapathogeninvadesthebody,itsantigensare
recognizedbyasmallfractionofthebody’sBcellsthatgrowanddividerapidly.TheyproduceplasmacellsandmemoryBcells.
• PlasmaCellsreleaseantibodies.Antibodiesareproteinsthatrecognizeandbindtoantigens.– AntibodieshaveaYshapeandsmalldifferencesin
theaminoacidsequencesthataffecttheshapeoftheirbindingsites.
– Thisallowsforthemtorecognizeavarietyofantigens.
– Itisestimatedthatahealthyadultcanproduceover100milliondifferenttypesofantibodies!
• Oncethebodyhasbeenexposedtoanantigen,millionsofmemoryBcellsremaintocreatemoreantibodiesspecifictothatantigen.Ifthebodyisexposedasecondtime,asecondaryresponseoccurswhichismustfastertoproduceplasmacellsandantibodies.
SpecificDefense:Cell-MediatedImmunity
• Thebody’sprimarydefenseagainstitsowncellswhentheyhavebecomecancerousorvirallyinfectedisknownascell-mediatedimmunity.Itisalsousedwhenfightinginfectioncausedbyprotistsorfungi.
• TcellsdivideanddifferentiateintokillerTcells(cytotoxicTcells),suppressorTcells,helperTcells,andmemoryTcells.– KillerTcellstrackdownanddestroy.– SuppressorTcellsreleasesubstancesthatshutdownthekillerTcellsoncetheinfectionisundercontrol.
– HelperTcellsproducememoryTcells.– MemoryTcellswillcauseasecondaryresponseifinfectedwiththesamepathogenagain.
AcquiredImmunity
• Morethan200yearsago,EdwardJennerwantedtoknowifitmightbepossibletoproduceimmunityagainstsmallpox.
• JennerknewofasimilardiseasecalledCowpoxcontractedbymilkmaids.
• Hewonderedifinfectingpeoplewithcowpoxwillprotectthemagainstsmallpox?
• HetriedthisonaboynamedJamiePhipps,anditworked!Thisisthefirstknownrecordofavaccination.
ActiveImmunity
• Theinjectionofaweakenedormildformofapathogentoproduceimmunityisknownasvaccination.– VaccaisthelatinwordforCowreflectingJenner’sexperiment
200yearsago!– Morethan20serioushumandiseasescanbepreventedby
vaccination.• Thetypeofimmunityproducedbythebody’sreactiontoa
vaccinationiscalledactiveimmunity.– Itcanalsocomenaturallyfromexposuretoanantigen(fighting
aninfection.)
PassiveImmunity• Ifantibodiesareproducedbyotheranimalsagainsta
pathogenareinjectedintothebloodstream,theantibodiesproduceapassiveimmunityagainstthepathogen.
• Passiveimmunitylastsonlyashorttimebecauseeventuallythebodydestroystheforeignantibodies.• Itcanalsocomefromaninfantbreastfeeding(mothersmilkcontains
essentialantibodies).Itprotectsthechildinthefewfirstmonthsofitslifeoruntilnolongerbreastfed.
• Alsoifyouareimmunizedbeforeatriptoadevelopingcountrywithtropicaldiseases,youmaybeimmunizedbeforeyouleave.Thisimmunitygoesawayovertime.
ImmuneSystemDisorders• Themostcommonoverreactionofthe
immunesystemistoantigensareknownasallergies.– Includepollen,beestings,dust,mold,etc
• Whenallergy-causingantigensenterthebody,theyattachthemselvestomastcells.Mastcellsarespecializedimmunesystemcellsthatinitiatetheinflammatoryresponse.Thecellsthenreleasechemicalsknownashistamines.
• Histaminesincreasethebloodflowandfluidstotheareaandincreasemucusproduction,causingtypicalsymptoms.– Therearemanyantihistaminesyoucantaketo
reducesymptomsofwateryeyes,runnynose,etc.
• Severeallergicreactionsmaycauseadangerousconditionknownasasthma.Asthmaisachronicrespiratorydiseaseinwhichtheairpassagesbecomenarrowerand/orinflamed.
AutoimmuneDiseases
• Theimmunesystemcouldnotdefendyourbodyagainstahostofinvadingpathogensunlessitwasabletodistinguishpathogensfromthecellsandtissuesthatareapartofyourownbody.Itneedstodeterminewhatis“self”and“non-self.”
• Whentheimmunesystemmakesamistakeandattacksthebody’sowncells,itproducesanautoimmunedisease.Theimmunesystemcreates“antiself”antibodies.
• Examples:TypeIdiabetes,MultipleSclerosis(MS),Lupis,Rheumatoidarthritis
AIDS:anImmunodeficiencyDisease• HIVisavirusthatdestroyshelperTcells.Asaresult,thenumberofhelperTcellsdecreasesandtheimmuneresponsebreaksdowncausingaconditioncalledAIDS.
• HIVisverydevastatingbecauseitevadestheimmunesystem(evolvesveryrapidly)andthendestroysitpreventingthebodyfrombeingabletodefendagainstotherpathogens.
• AIDSstandsfor:Acquiredimmunedeficiencysyndrome
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