Identification ofamonoclonal antibody specific for

A monoclonal antibody (145-2C11) specific forthemurineT3complex wasderived byimmunizing Armenian hamsters withamurine cytolytic T-cell clone. The antibody isspecific fora25-kDa protein component (T3-e) of theantigen-specific T-cell receptor. Itreacts withall mature T cells andcanbothactivate andinhibit T-cell function. These results identify T3-Easacell surface protein involved inthe transduction ofactivation signals. Activation ofmature Tcells isaprocess that requires both receptor occupancy byforeign antigen inthecontext ofmajor histocompatibility complex (MHC)proteins andtransduction ofatransmembrane signal. Thespecific antigen recognition hasbeenshowntobedependent ona disulfide-linked heterodimer containing twointegral membrane glycoprotein chains, a(45-50 kDa)and/(40-44 kDa)(1). Theaand/3 chains areencoded byfamilies ofgenes, giving rise toa polymorphic setofcell membrane receptors clonally ex- pressed onTlymphocytes. Dembic etal. (2) andSaito etal. (34) havedemonstrated that transfection andexpression of thegenes encoding theaBheterodimer results intheacqui- sition ofMHC-restricted antigen recognition, establishing the direct relationship ofantigen specificity toaBexpression. Thesecond step ofT-cell activation (transmembrane signal- ing) ispresently thought tobemediated byaninvariant complex ofproteins (T3) thatbyimmunoprecipitation has beenshowntobenoncovalently associated withtheaf3 heterodimer intheT-cell receptor (TCR) complex (3, 4). The