We have isolated T cell receptor (TCR) cDNAs from fluorescein (FL)-specific human T cell clones (αFLβFL.), and transferred them to TCR β- Jurkat cells in order to study direct FL-binding to the TCR. Using either FLconjugated polymers (FL-polymer) or FL-substituted Sepharose beads, we are able to demonstrate the direct binding of antigen to the T cell surface, and the functional activation of the T cell transfectants. We present evidence against the involvement of major histocompatibility complex (MHC) molecules or antigen presentation in the interaction of FL with the αFLβFL transfectants. Additionally, we have examined the effect of ring substitutions on the FL molecule as well as specific alterations of substituents attached to the 5' position, and we have found that all of them interfere with the functional recognition of the αFLβFL TCR. These experiments demonstrate that TCRs like antibodies have intrinsic affinities for antigen, even without the involvement of MHC molecules.
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