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