ABSTRACT
Primaryevent.TheprimaryeventintheTI-GVHDmodelappearstobetheactivationof effectormechanism(s)thatcauseacuteGVHDtissuedestruction.Tcellsfromthetransfusion graftmayreactwitheitherclassI(33)orclassII(109)alloantigensintherecipient.ClassII antigensarepresentonantigen-presentingcells(APCs)(macrophages,monocytes,epidermal Langerhans'cells,vascularendothelialcells,anddendriticcellsinlymphoidorgans),onB lymphocytes,onthymicepithelialcells,andonactivatedTlymphocytes(112).ItistheCD4+ TlymphocytethatrecognizesclassIIHLAdifferences,whereasCDS+Tlymphocytes apparentlyareresponsibleforGVHDwhenHLAclassIalloantigensstimulatethereaction (113-115).WhencompleteMHCdifferencesexist(bothclassIandclassIIforeignness),either CD4+orCDS+cellscanapparentlyinitiateGVHD(116).
