ROLE OF THE CDR1 REGION OF THE TCR BETA-CHAIN IN THE BINDING TO PURIFIED MHC-PEPTIDE COMPLEX

Single alanine substitutions were introduced into the CDR1 region of t he beta chain of a K-d-restricted TCR. Mutants and wild-type TCR were attached to the zeta chain of the CD3 complex and expressed at the sur face of a rat basophil cell line. Transfectants were tested for the bi nding of purified soluble K-d-peptide complexes. With this experimenta l system, accessory molecules are unlikely to play a major role and th e contribution of each residue to the interaction can be addressed. Re sults show that all positions in the CDR1 region are involved in the b inding to the K-d-peptide complex but at varying degrees. These effect s are discussed in relation to a molecular model of the TCR. Compariso n of these results with previous data obtained in a T cell hybridoma s ystem suggests the existence of a threshold in the TCR affinity necess ary for mature T cell activation.