Constitutive CD30 expression expands PCs in vivo and in vitro. (A) Serum concentrations of total immunoglobulins of the indicated isotypes were determined by enzyme-linked immunosorbent assay. Horizontal bars represent mean values. (B) Quantitative reverse transcription polymerase chain reaction analysis showing the relative expression of Prdm1 (BLIMP1), Xbp1, and Pax5 in CD43⁺CD23^low B1 vs CD43⁻CD23⁺ B2 cells from control (ctrl) and LMP1/CD30 mice. Expression was standardized to the housekeeping gene Ywhaz. (C) Relative mean fluorescence intensity (MFI) of IRF4 in B1 (CD43⁺CD23^low) and B2 cells (CD43⁻CD23⁺) from LMP1/CD30 and ctrl mice. Relative MFIs were related to the MFI of ctrl B2 cells, which was set as 1. Data are from 3 independent experiments. (D) B1 (CD43⁺CD23^low) and B2 cells (CD43⁻CD23⁺) were analyzed for their CD138/B220 expression and shown as an overlay (n ≥ 4). (E) B1 cells (CD43⁺CD23^low) were sorted and reanalyzed as described in supplemental Figure 6. CD138⁺B220^low cells were excluded in the sorted population. After sorting, B1 cells (CD138⁻CD43⁺CD23^low) were cultivated without stimulation for 3 days and subsequently analyzed for their CD138/B220 expression. The dot plots show the gating strategy, and the graph compiles data of percentages of CD138^highB220^low cells from the indicated genotypes from 3 independent experiments. *P < .05, **P < .01, ****P < .0001. ns, not significant.