Further characterization of the lectin/ligand complex was performed by isothermal titration calorimetry of L-SIGN with Man84 (Fig. ). Triplicate measurements by ITC determined an equilibrium dissociation constant KD of 12.7 μM ± 1 μM with a 1.1 stoichiometry of binding. This is in full agreement with the IC50 evaluated above from the SPR competition experiments. It is striking to find such an increase in affinity by a factor of 230, compared to the natural mannose residue, resulting from this unique modification in C2 .