Association and dissociation of a strongly-binding antibody with different surface densities of VAR2CSA DBL5ε. The frequency shift (Hz) is shown as a function of time (s). Black lines represent data from different reactions, with the indicated concentrations of PAM 3.10 binding to VAR2CSA DBL5ε immobilized on a carboxyl surface. Red lines indicate the fitted curves, as described in the Methods. The rate constants calculated are given on the sensorgram. A. PAM 3.10, in flow, against a high density surface. B. PAM 3.10, in flow, against a low density surface. See Additional file 1 for surface antigen density calculations.