TheIGF-IIELISAiscalibratedagainsttheInternationalStandard:WHONIBSC96/538.

ThestandardsoftheELISAarehumanIGF-IIinconcentrations0.45;1.5;3;5.63and9ng/ml,respectivelytheassayrangecovers–atrecommendednormalsampledilution-therangeto2400ng/ml.Byvaryingthesampledilutionthiscanbeadaptedtothespecialindividualrequirements.

Sensitivity
TheanalyticalsensitivityoftheELISAyields0.02ng/ml(2SDofzerostandardin20folddetermination).
TheInter-andIntra-Assayvariationcoefficientsarelessthan7.2%and6.6%respectively.

INTENDEDUSE
Scientificinvestigationsinthefieldofneonatalhypertrophy(IGF-IIisafoetalgrowthfactor)andmalignancies(IGF-IIisamonogenicgrowthfactor).

IGF-IIseemstobeofuseindifferentialdiagnosticsofmalignancies.Thus,itispossIBLetodifferentiatebyIGF-IIbetweenadrenocorticalcarcinomasandadenomas.FurthertumorstaginganddifferentiationbetweenhyperplasiaandcarcinomacanbeimprovedbyIGF-IImeasurementsinprostatetumors.TheIGF-Systemseemtobeofrelevanceinneurodegenerationaswell,e.g.Alzheimer´sandParkinson’sdiseases.


Theinsulin-likegrowthfactors(IGF)-Iand–IIplayapivotalroleintheregulationofproliferationanddifferentiationofseveraltissuetypes.IGF-IalsocalledSomatomedinChasamolecularweightof7.469kDa.ItsexpressionismainlyregulatedbyGrowthHormoneandnutrition.ButseveralhormonesandpeptidefactorsareknowntoinfluenceIGF-IIsynthesisindifferenttissues.BioavailABIlityoftheIGFsisregulatedbyspecificbindingproteins(IGFBP).BesidethehighaffinityInsulin-likeGrowthFactorBindingProteins1-6,IGFsarealsoboundbeIGFBP-relatedProteins.ThesebindingproteinsbindIGF-IandIGF-IIwiththesameaffinityorpreferIGF-II.DirectmeasurementofIGFsinserumsampleswithoutpretreatmentresultsinfalsevaluesbecauseoftheextremelyslowdissociationoftheIGF/IGFBPcomplexesduringtheassayincubationonlyapartoftheIGF-IIinthespecimencanbindtotheantibodiesandbedetected.

Therefore,varioustechniqueswereappliedtophysicallyseparateIGF-IIfromitsbindingproteinsbeforemeasurement,including(a)sizeexclusionchromatographyunderacidicconditions,(b)solid-phaseextractionand(c)acid-ethanolextraction.Thesetechniques,however,areeitherinconvenientortime-consumingorgiveincompleteandnot-reproduciblerecoveries.

Thisassayiseasy,fastandresultsdonotdependonthebindingproteinconcentrationofthesample.ItisbasedonthehighspecificityoftheemployedantibodiesforIGF-II.Thereisvirtuallynocross-reactivitywithIGF-I.ThisallowstheseparationofIGF-IIfromthebindingproteinsbyacidificationandblockingofthefreebindingproteinswithIGF-I.Thus,theendogenousIGF-IIisfreeinsolution.