Proteasome inhibition alters the intracellular distribution of persisting antigen-BCR complexes. (A) MD4.B10.Br splenocytes were pretreated with the indicated inhibitor for 1 hour at 37°C before pulsing with antigen (100 nM HEL) for 4 hours. The cells were then washed (to remove both antigen and drug) and cultured for an additional 18 to 20 hours at 37°C. The cells were then collected, fixed, and stained for persisting Ag-BCR complexes using the 2D1 anti-HEL mAb.^11,14  C indicates control, non–drug-treated cells; M, MG-132–treated cells; and L, lactacystin-treated cells. Shown are representative images from 1 of 4 independent experiments. (B) For each experimental condition, 100 B cells were visualized and the distribution of persisting antigen was scored as described in “Material and methods.” Shown is the frequency of cells in which the persisting Ag-BCR complexes were detected in 1, 2, 3, or 4 quadrants of the cell. Each bar represents the results from a single independent experiment.