PHOTOAFFINITY-LABELING OF THE T-CELL RECEPTOR ON LIVING CYTOTOXIC T-LYMPHOCYTES

Using a direct binding assay based on photoaffinity labeling, we have studied the interaction of an antigenic peptide with MHC class I molec ules and the TCR on living cells. Two photoreactive derivatives of the H-2K(d) (Kd) restricted Plasmodium berghei circumsporozoite (PbCS) pe ptide 253-260 (YIPSAEKI) were used. The first derivative contained an N-terminal photoreactive iodo, 4-azido salicyloyl (IASA) group and bio tin on the TCR contact residue LyS259 [IASA-YIPSAEK(biotin)I]. As prev iously described, this derivative selectively bound to and labeled the K(d) molecule. The second photoreactive compound, the isomeric biotin -YIPSAEK(IASA)I, also efficiently bound to the K(d) molecule, but fail ed to label this protein. A CTL clone derived from a mouse immunized w ith this derivative recognized this conjugate but not the parental P b ergheicircumsporozoite peptide or the [/ASA-YIPSAEK-(biotin)I] derivat ive in an K(d)-restricted manner. Incubation of the cloned CTL cells w ith biotin-YIPSAEK(IASA)I, but not its isomer, followed by UV irradiat ion resulted in photoaffinity labeling of the TCR-alpha chain that was dependent on the conjugate binding to the K(d) molecule. The TCR labe ling was partially inhibited by anti-LFA 1 and anti-ICAM1 mAb, but was increased by addition Of beta2m or soluble K(d)Q10. The exquisite lab eling selectivity of the two photoprobes opens a new, direct approach to the molecular analysis of antigen presentation and recognition by l iving CTL.