Advances in artificial immune systems

SearchMethodologies:IntroductoryTutorialsinOptimizationandDecisionSupportTechniquesEdmundK.Burke(Editor),GrahamKendall(Editor)Chapter13ARTIFICIALIMMUNESYSTEMSU.Aickelin#andD.Dasgupta*#UniversityofNottingham,NottinghamNG81BB,UK*UniversityofMemphis,Memphis,TN38152,USA1.INTRODUCTIONThebiologicalimmunesystemisarobust,complex,adaptivesystemthatdefendsthebodyfromforeignpathogens.Itisabletocategorizeallcells(ormolecules)withinthebodyasself-cellsornon-selfcells.Itdoesthiswiththehelpofadistributedtaskforcethathastheintelligencetotakeactionfromalocalandalsoaglobalperspectiveusingitsnetworkofchemical2messengersforcommunication.Therearetwomajorbranchesoftheimmunesystem.Theinnateimmunesystemisanunchangingmechanismthatdetectsanddestroyscertaininvadingorganisms,whilsttheadaptiveimmunesystemrespondstopreviouslyunknownforeigncellsandbuildsaresponsetothemthatcanremaininthebodyoveralongperiodoftime.Thisremarkableinformationprocessingbiologicalsystemhascaughttheattentionofcomputerscienceinrecentyears.Anovelcomputationalintelligencetechnique,inspiredbyimmunology,hasemerged,calledArtificialImmuneSystems.Severalconceptsfromtheimmunehavebeenextractedandappliedforsolutiontorealworldscienceandengineeringproblems.Inthistutorial,webrieflydescribetheimmunesystemmetaphorsthatarerelevanttoexistingArtificialImmuneSystemsmethods.Wewillthenshowillustrativereal-worldproblemssuitableforArtificialImmuneSystemsandgiveastep-by-stepalgorithmwalkthroughforonesuchproblem.AcomparisonoftheArtificialImmuneSystemstootherwell-knownalgorithms,areasforfuturework,tips&tricksandalistofresourceswillroundthistutorialoff.ItshouldbenotedthatasArtificialImmuneSystemsisstillayoungandevolvingfield,thereisnotyetafixedalgorithmtemplateandhenceactualimplementationsmightdiffersomewhatfromtimetotimeandfromthoseexamplesgivenhere.2.OVERVIEWOFTHEBIOLOGICALIMMUNESYSTEMThebiologicalimmunesystemisanelaboratedefensesystemwhichhasevolvedovermillionsofyears.Whilemanydetailsoftheimmunemechanisms(innateandadaptive)andprocesses(humeralandcellular)areyetunknown(eventoimmunologists),itis,however,well-knownthattheimmunesystemusesmultilevel(andoverlapping)defensebothinparallelandsequentialfashion.Dependingonthetypeofthepathogen,andthewayitgetsintothebody,theimmunesystemusesdifferentresponsemechanisms(differentialpathways)eithertoneutralizethepathogeniceffectortodestroytheinfectedcells.Adetailedoverviewoftheimmunesystemcanbefoundinmanytextbooks,forinstanceKubi(2002).Theimmunefeaturesthatareparticularlyrelevanttoourtutorialarematching,diversityanddistributedcontrol.Matchingreferstothebindingbetweenantibodiesandantigens.Diversityreferstothefactthat,inordertoachieveoptimalantigenspacecoverage,antibodydiversitymustbeencouragedaccordingtoHightoweretal(1995).Distributedcontrolmeansthatthereisnocentralcontroller;3rather,theimmunesystemisgovernedbylocalinteractionsamongimmunecellsandantigens.Twoofthemostimportant-cellsinthisprocessarewhitebloodcells,calledT-cells,andB-cells.Bothoftheseoriginateinthebonemarrow,butT-cellspassontothethymustomature,beforetheycirculatethebodyinthebloodandlymphaticvessels.TheT-cellsareofthreetypes;ThelpercellswhichareessentialtotheactivationofB-cells,KillerT-cellswhichbindtoforeigninvadersandinjectpoisonouschemicalsintothemcausingtheirdestruction,andsuppressorT-cellswhichinhibittheactionofotherimmunecellsthuspreventingallergicreactionsandautoimmunediseases.B-cellsareresponsiblefortheproductionandsecretionofantibodies,whicharespecificproteinsthatbindtotheantigen.EachB-cellcanonlyproduceoneparticularantibody.TheantigenisfoundonthesurfaceoftheinvadingorganismandthebindingofanantibodytotheantigenisasignaltodestroytheinvadingcellasshowninFigure1.4APCMHCproteinAntigenPeptideT-cellActivatedT-cellB-cellLymphokinesActivatedB-cell(plasmacell)(I)(III)(IV)(V)(VI)(VII)(II)Figure-1.Pictorialrepresentationoftheessenceoftheacquiredimmunesystemmechanism(takenfromdeCastroandvanZuben(1999):I-IIshowtheinvadeenteringthebodyandactivatingT-Cells,whichtheninIVactivatetheB-cells,Vistheantigenmatching,VItheantibodyproductionandVIItheantigen’sdestruction.Asmentionedabove,thehumanbodyisprotectedagainstforeigninvadersbyamulti-layeredsystem.Theimmunesystemiscomposedofphysicalbarrierssuchastheskinandrespiratorysystem;physiologicalbarrierssuchasdestructiveenzymesandstomachacids;andtheimmunesystem,whichhascanbebroadlydividedundertwoheads–Innate(non-specific)ImmunityandAdaptive(specific)Immunity,whichareinter-linkedandinfluenceeachother.TheAdaptiveImmunityagainissubdividedundertwoheads–HumoralImmunityandCellMediatedImmunity.InnateImmunity:TheInnateImmunityispresentatbirth.PhysiologicalconditionssuchaspH,temperatureandchemicalmediatorsprovideinappropriatelivingconditionsforforeignorganisms.Alsomicroorganismsarecoatedwithantibodiesand/orcomplementproducts(opsonization)sothattheyareeasilyrecognized.Extracellularmaterialistheningestedbymacrophagesbyaprocesscalledphagocytosis.AlsoTDHCellsinfluences5thephagocytosisofmacrophagesbysecretingcertainchemicalmessengerscalledlymphokines.Thelowlevelsofsialicacido