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1、Chapter24Pathogens,Infection,andInnateImmunity24Infectiousdiseasescurrentlycauseaboutone-thirdofallhumandeathsintheInThisChapterworld,morethanallformsofcancercombined.Inadditiontothecontinuingheavyburdenofancientdiseasessuchastuberculosisandmalaria,n
2、ewinfec-INTRODUCTIONTO1486tiousdiseasesarecontinuallyemerging,includingthecurrentpandemic(world-PATHOGENSwideepidemic)ofAIDS(acquiredimmunedeficiencysyndrome),whichhasalreadycausedmorethan25milliondeathsworldwide.Moreover,somedis-CELLBIOLOGYOF1501eas
3、eslongthoughttoresultfromothercausesarenowturningouttobeassoci-INFECTIONatedwithinfections.Mostgastriculcers,forexample,arecausednotbystressorBARRIERSTO1524spicyfood,aswasoncebelieved,butbyabacterialinfectionofthestomachINFECTIONANDTHEcausedbyHelicob
4、acterpylori.INNATEIMMUNESYSTEMTheburdenofinfectiousdiseasesisnotspreadequallyacrosstheplanet.Poorercountriesandcommunitiessufferdisproportionately.Frequently,theprevalenceofinfectiousdiseasescorrelateswithpoorpublicsanitationandpublichealthsystems,wh
5、ichareoftenfurthercompromisedbynaturaldisastersorpoliticalupheavals.Someinfectiousdiseases,however,occurprimarilyorexclusivelyamongindustrializedcommunities:Legionnaire’sdisease,com-monlyspreadthroughair-conditioningsystems,isarecentexample.Humanshav
6、elongbeenbothtroubledandfascinatedwithinfectiousdis-eases.Theearliestwrittendescriptionsofhowtolimitthespreadofrabiesdatebackmorethan3,000years.Sincethemid-1800s,physiciansandscientistshavestruggledtoidentifytheagentsthatcauseinfectiousdiseases,colle
7、ctivelycalledpathogens.Morerecently,theadventofmicrobialgeneticsandmolecularcellbiologyhasgreatlyenhancedourunderstandingofthecausesandmechanismsofinfectiousdiseases.Wenowknowthatpathogensfrequentlyexploitthebio-logicalattributesoftheirhost’scellsino
8、rdertoinfectthem.Thisunderstandingcangiveusnewinsightsintonormalcellbiology,aswellasstrategiesfortreat-ingandpreventinginfectiousdiseases.Inaworldteemingwithhostile,subtle,andrapidlyevolvingpathogens,howdoesafragileandslowlyevolvinghumansurvive?Likea
