To do so, T cells have a very high degree of antigen specificity, despite of fact that the affinity to the peptide/MHC ligand is rather low in comparison to other receptor types. The affinity, given as the dissociation constant ("K"d), between a TCR and a pMHC was determined by surface plasmon resonance (SPR) to be in the range of 1-100 μM, with an association rate ("k"on) of 1000 -10000 M−1 s−1 and a dissociation rate ("k"off) of 0.01 -0.1 s−1. In comparison, cytokines have an affinity of KD = 10-600 pM to their receptor.