High-rate proliferation of reactive plasma cells is rapidly downregulated. Freshly explanted cells were incubated for 2 hours with 1 mmol/L BrdU at day 0 and at day 2 or 3, as indicated in the figure. BrdU⁺ cells were determined in the intracytoplasmic (c) λ or κ population by double staining with anti-λ-PE or anti-κ-PE MoAb versus FITC-anti-BrdU MoAb, as described in Materials and Methods. For each dot-plot, 10,000 events were acquired. Dot-plots: A, RP9; B, RP7.