Immunity
Volume 10, Issue 2, February 1999, Pages 219-225
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Article
T Cell Receptor and Coreceptor CD8αα Bind Peptide-MHC Independently and with Distinct Kinetics

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Abstract

The T cell surface glycoprotein CD8 enhances T cell antigen recognition by binding to MHC class I molecules. We show that human CD8αα binds to the MHC class I molecule HLA-A2 with an extremely low affinity (Kd ∼0.2 mM at 37°C) and with kinetics that are between 2 and 3 orders of magnitude faster than reported for T cell receptor/peptide-MHC interactions. Furthermore, CD8αα had no detectable effect on a T cell receptor (TCR) binding to the same peptide-MHC class I complex. These binding properties provide an explanation as to why the CD8/MHC class I interaction is unable to initiate cell-cell adhesion and how it can enhance TCR recognition without interfering with its specificity.

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