TheaimofthisstudyistofindtheexperimentalevidencethattheprecursorfrequencyofalloreactiveCTLsisproportionaltothenumberoftheT-cellepitopespecificities.ThenumberofT-cellepitopespecificitieswasmanipulatedbypulsingdifferentnumberofHLA-A2restrictedpeptide(s)ontotheT2cells,whichactedasstimulatingcellstoelicitallo-reactionbyco-culturingwithperipheralbloodlymphocytes(PBLs)ofHLA-A2negativeinpidual.TenHLA-A2restrictedpeptides(allwerenormalcellcomponents)weresynthesized,andcellpeptideextractwaspreparedbyfrozenandthawed.T2cellsloadedwithdifferentnumberofpeptide(s)wereco-culturedwithPBLsofanHLA-A2negativeinpidual;thelatterwerestainedwithPKH67inadvance.Thentheproliferationwasmonitoredwithflowcytometry,andtheprecursorfrequencyoftheeffectorcellswasanalyzedbytheModFitSoftware.After6dofculture,noproliferationwasobservedinthebulkcultureofPBLalone,andobviousproliferationtookplacewhenPBLsoftheHLA-A2negativewereco-culturedwithT2cellsloadedwithorwithoutloadingpeptide(s).TheprecursorfrequencyofthealloreactiveCTLswas0.052819forco-culturewithT2cellsloadedwithoutpeptide;howeveritwas0.030429forT2cellswithEBV/LMP2Aand0.030528forT2cellsloadedwithasingleautogeneicpeptide,andincreasedupto0.144942forT2cellsloadedwith10autogeneicpeptides;theprecursorfrequencywas0.203649whenco-culturedwithT2cellsloadedwithmiscellaneouspeptidesextractedfromthecytoplasmofT2cells.ThisstudyrevealsthattheprecursorfrequencyofalloreactiveCTLsisproportionaltothenumberofT-cellepitopespecificities,andindependentofthedensityoftheallogeneicHLAClassⅠmolecule.OurfindingssupportthehypothesisthatthealloreactiveTcellpopulationscomprisemiscellaneousTcellclones;eachisspecifictocorrespondingpMHC.ThenovelconstellationofpeptidespresentedbyallogeneicMHCmoleculesmakesthous
