Figure 2. Outline of SPR-based gp120/Env interaction assays. (a) The gp120-sCD4 interaction. In this assay, either of the interactants can be immobilized on the sensor surface. (b) The gp120-mAb 17b interaction. mAb 17b is immobilized on the sensor surface. This is because mAb 17b is a conformationally sensitive antibody and does not recognize the immobilized gp120. (c) CD4-gp120-mAb 17b interaction. As with the direct binding of gp120 and mAb 17b, mAb 17b is immobilized.