Development of a Fluorescence Anisotropy Assay for Measuring the TCR-pMHC Interaction

Cytotoxic T cells destroy virally infected cells and tumor cells and are also implicated in transplant rejection. These cells are also known as CD8+ T cells, since they express the CD8 glycoprotein at their surface. The T cell receptor (TCR) is a molecule found on the surface of T cells that is responsible for recognizing antigens presented by major histocompatability complex (MHC) proteins. MHC proteins are expressed on the surface of cells and display fragments of molecules from invading microbes or dysfunctional cells to the TCR. Measurements of TCR-pMHC binding equilibrium and kinetic parameters have been obtained through the utilization of surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC). Unlike pure solution methods, SPR does not allow for detailed resolution of the kinetic mechanism for the TCR-pMHC interaction, which can be obtained from stopped-flow fluorescence anisotropy. The need for such an assay is essential to understanding the recognition mechanism of the TCR as well as enabling further investigation of TCR cross reactivity and specificity. Fluorescence studies of the TCR-pMHC interaction were completed using a fluorescein derivative to label an MHC free cysteine via maleimide chemistry. Current data with the A6 T cell receptor and the Tax peptide presented by the class I MHC HLA-A2 shows that as the concentration of A6 increases, the pMHC is bound resulting in an increased anisotropy. This trend is seen in various A6 constructs (A6 wild-type and A6 c134 zippered constructs, Cole /Sewell A6 wild-type and A6 c134) that have been studied. Once we have determined that an anisotropy reading is observed using our fluorescein derivitized protein we can utilize various peptides and their corresponding TCRs to determine their unique kinetic parameters and recognition mechanism.