adult peripheral blood proliferated whenstimulated bytheprotease-sensitive component ofmycobacterial organisms orpurified protein derivative, confirming thatadult Tcells respond toprotein components whereas cordblood T cells respond tothenonpeptide component ofmycobacteria. Invitro culture ofcordbloodlymphocytes stimulated byeither mycobacterial lysates or thelipid fraction showedincreases inthenumbersofT-cell receptor (TcR)-y/6 Tlymphocytes with nochanges inthenumbers ofTcRaLlp Tlymphocytes incontrast tothe invitro cultures ofadult blood lymphocytes stimulated withmycobacterial ligands inwhichno increase ofTcR ,y/8 cellswas observed. Interleukin-2 receptor (CD25)andIaantigen (HLA-DR)analyses evidenced the activation ofa largeproportion ofcordbloody/8T cells whichhadincreased afterstimulation with mycobacteria invitro. Further characterization ofmycobacterial ligand suggested thatthelipid fraction of mycobacterial lysate ortrehalose dimycolate-cord factor was themostplausible causeforT-cell proliferation incordblood. Theseresults suggest thatwhenthey/8 T cells ina newborninfant notyetsensitized toany pathogenic organisms areconfronted bya mycobacterium, theyrespond nonspecifically tothemycobacterial organism oritslipid component (cord factor). y/8Tcells may therefore play adistinct roleinforming thefirst line ofthehostdefense systemagainst certain microorganisms. Protective immunity against microbial organisms ismediatedbybothhumoral andcellular immunity. Duringthe newbornperiod inhumans,immunoglobulin G antibodies whichare passively transferred intothefetusfromthe motherthrough theplacenta playan important rolein protective immunity. Todate, no evidence ofpassive transferoflymphocytes fromthemothertothefetusviathe placenta hasbeenreported, makingcordbloodlymphocytes thelogical choice forinvestigating thecellular mechanism of thefirst lineofthehostdefense against various pathogenic microorganismsinhumans.
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