Affinity and kinetics of the interactions between an αβ T-cell receptor and its superantigen and class II-MHC/peptide ligands

Immune activation is mediated by a specific interaction between the T-cell receptor (TCR) and an antigenic peptide bound to the major histocompatibility complex (MHC). T-cell activation can also be stimulated by superantigens which bind to germline-encoded variable domain sequences of certain TCR β-chains. We have used a surface plasmon resonance biosensor to characterize the molecular interactions between a class II-restricted αβ TCR and its superantigen and MHC/peptide ligands. The extracellular domains of the murine D10 TCR (Vα2, Vβ8.2) were expressed in insect cells and secreted as a disulfide-linked heterodimer. In the absence of MHC class II, purified soluble D10 TCR bound to Staphylococcus aureus enterotoxin C2 with an association rate of 1.69 ± 0.12 × 10 4 M −1 sec −1 and a dissociation rate of 1.9 ± 0.47 × 10 −2 sec −1, giving a dissociation constant of 1.1 μM. Binding of the TCR to S. aureus enterotoxin B was barely detectable and could not be measured accurately due to the rapid dissociation rate. Soluble D10 TCR also bound to a soluble murine MHC class II I-A k molecule containing a fused antigenic conalbumin peptide and complementary leucine zipper sequences to facilitate efficient chain pairing. The purified I-A k chimera specifically stimulated proliferation of the D 10 T-cell clone, and bound to immobilized soluble D10 TCR with an association rate of 1.07 ± 0.19 × 10 4 M −1 sec −1 and a dissociation rate of 2.2 ± 0.65 × 10 −2 sec −1, giving a dissociation constant of 2.1 μM.