ALPHA-BETA-T-CELL RECEPTOR INTERACTIONS WITH SYNGENEIC AND ALLOGENEICLIGANDS - AFFINITY MEASUREMENTS AND CRYSTALLIZATION

Cellular immunity is mediated by the interaction of an alpha beta T ce ll receptor (TCR) with a peptide presented within the context of a maj or histocompatibility complex (MHC) molecule. Alloreactive T cells hav e alpha beta TCRs that can recognize both self- and foreign peptide-MH C (pMHC) complexes, implying that the TCR has significant complementar ity with different pMHC. To characterize the molecular basis for allor eactive TCR recognition of pMHC, we have produced a soluble, recombina nt form of an alloreactive alpha beta T cell receptor in Drosophila me lanogaster cells. This recombinant TCR, 2C, is expressed as a correctl y paired alpha beta heterodimer, with the chains covalently connected via a disulfide bond in the C-terminal region. The native conformation of the 2C TCR was probed by surface plasmon resonance (SPR) analysis by using conformation-specific monoclonal antibodies, as well as synge neic and allogeneic pMHC ligands. The 2C interaction with H-2K(b)-dEV8 , H-2K(bm3)-dEV8, H-2K(b)-SIYR, and H-2L(d)-p2Ca spans a range of affi nities from K-d = 10(-4) to 10(-6) M for the syngeneic (H-2K(b)) and a llogeneic (H-2K(bm3), H-2L(d)) ligands. In general, the syngeneic liga nds bind with weaker affinities than the allogeneic ligands, consisten t with current threshold models of thymic selection and T cell activat ion. Crystallization of the 2C TCR required proteolytic trimming of th e C-terminal residues of the alpha and beta chains. X-ray quality crys tals of complexes of 2C with H-2K(b)-dEV8, H-2K(bm3)-dEV8 and H-2K(b)- SIYR have been grown.