T-cell proliferation after priming with DC that were pulsed with the indicated reagents. DC were unpulsed or loaded with the soluble A20 Ig idiotype, with A20 cells, with a soluble heterodimeric A20 Ig idiotype containing the anti-FcR binding arm or with BiV cells. For blocking FcR-mediated Ag uptake during coincubation with BiV cells, the anti-FcR mAb 2.4G2 was added. Proliferation of T cells was determined by 3H-thymidine uptake. Proliferation indices were calculated by normalizing the radioactivity incorporated in T cells to the background levels without T cells. The bars represent results at a T cell/DC ratio of 9:1. Mean values and standard deviations are compiled from 3 experiments.