T cell receptor-MHC class I peptide interactions: affinity, kinetics, and specificity

Area of Science:

• Immunology
• Molecular Biology
• Biochemistry

Background:

• T cell activation is critical for adaptive immunity.
• T cell receptors (TCRs) recognize peptide-major histocompatibility complex (MHC) complexes on antigen-presenting cells.
• Understanding the kinetics of TCR-peptide-MHC interactions is key to deciphering T cell signaling.

Purpose of the Study:

• To quantify the binding kinetics between a purified T cell receptor (TCR) and a specific murine MHC class I-peptide complex.
• To determine the association and dissociation rates, as well as the equilibrium constant, for this interaction.
• To infer the implications of these kinetic parameters for T cell activation thresholds.

Main Methods:

• Utilized surface plasmon resonance (SPR) for direct, real-time measurement of molecular binding.
• Employed purified soluble analog of murine MHC class I molecule (sH-2Ld) and a synthetic octamer peptide (p2CL).
• Measured kinetic association rate (kon), kinetic dissociation rate (koff), and calculated equilibrium dissociation constant (KD).

Main Results:

• The kinetic dissociation rate (koff) of the MHC-peptide complex from the TCR was rapid, approximately 2.6 x 10(-2) second(-1) (half-time ~27 seconds).
• The kinetic association rate (kon) was measured at 2.1 x 10(5) M(-1) second(-1).
• The equilibrium dissociation constant (KD) was calculated to be approximately 10(-7) M.

Conclusions:

• The rapid dissociation rate suggests that a single TCR-peptide-MHC interaction is transient.
• TCRs likely require engagement with multiple MHC-peptide complexes in a multivalent array to achieve stable binding and initiate T cell signaling.
• These findings provide quantitative insights into the molecular basis of T cell discrimination and activation.