DC-SIGNR adsorption was quantified from the change in the plasmon resonance angle measured after incubating the NTA-TRIG-DLGE monolayer with 0.5 μM of either of the 7-, 6-, or 5-repeat DC-SIGNR for 1.5 h at room temperature. The 1.5 h incubation time was also used to prepare samples for all surface force measurements in this study. The total protein adsorbed was determined from the change in the resonance angle and use of the 5-phase Fresnel calculation program (R. Corn, University of California, Irvine). The DC-SIGNR surface coverage was calculated from the effective refractive index of the protein monolayer n eff . This value is obtained from the measured optical thickness (product of the refractive index and layer thickness, n eff Â D T ). This measurement and the thicknesses D T determined from surface force measurements were used to obtain the effective refractive index n eff . Assuming a linear dependence of the refractive index on surface concentration, the surface coverage Γ (molecules/m 2 ) of the different DC-SIGNR variants was calculated from the refractive indices and use of a refractive index increment dn/dc of 0.187, where c is the surface concentration in mg/m 2 . 22, 23 The error in protein densities determined from refractive index measurements is ∼20%. 22, 23 This analysis differs slightly from that used previously (see Supporting Information). 18 The protein (tetramer) densities of the 7-repeat and 6-repeat forms are determined by dividing the monomer density by four. A similar calculation for the 5-repeat form is more complicated because it is expressed as a mixture of interconverting dimers and tetramers, with a solution dissociation constant of 0.14 μM, as determined by equilibrium analytical ultracentrifugation. 11 Whether this distribution persists on the membrane, particularly under applied force, cannot be easily determined. Nevertheless, the measured jumps into contact presented here indicate the presence of folded tetramers on the membrane.