Figure 6: IL-21 reversibly suppresses the differentiation of iGB cells into iMB cells.

(a) Flow cytometric analysis for CD19/Ly5.1 expression on the cells from indicated tissues of untreated C57BL/6 mice (B6) or recipient mice that received iGB-4, iGB-21, or iGB-m cells, each devoid of CD138⁻ cells and containing 1×10⁷ IgG1⁺ cells, 30 days before. The numbers indicate the percentage of iMB cells defined by each window. (b) The numbers of splenic iMB-4 (closed circles: n=15), iMB-21 (shaded circles: n=4) or iMB-m (open circles: n=8) cells were estimated by the analysis as shown in (a) in individual recipient mice on the indicated days. Difference is significant between the iMB-4 and iMB-m cells (**P<0.000006) and between iMB-m and iMB-21 cells (*P<0.01) from the recipient mice analysed by day 50 after transfer. Data from 11 experiments were combined. (c) iMB-4 and iMB-m cells (CD19⁺ Ly5.1⁺) in the spleens of mice generated as in (a) and in control CD19⁺ B cells from untreated B6 mice were analysed for expression of the indicated markers. The numbers indicate the percentage of cells defined by each window. (d) Expression of the indicated markers on the splenic iMB-4 (thick line), iMB-m (dotted line) or B6 naïve (shaded) B cells. (c,d) Data shown are representative of three or more independent experiments. (e) Splenic B cells of the recipient mice containing 8×10³ NP⁺ iMB-4 or iMB-m cells, or those of a B1-8 ki mouse containing 8×10³ NP⁺ naïve B cells (the numbers were estimated on the basis of their frequency in flow cytometric analyses), each supplemented with naïve B cells of untreated B6 mice to make the total B-cell number 2.4×10⁷, or splenic B cells (2.4×10⁷) of the recipient having received iGB-21 cells ('iGB-21 rcpt.'), were co-transferred with CGG-primed CD4⁺ T cells (T_mem) into γ-irradiated B6 mice. Seven days after i.v. immunization with NP₄₀-CGG, serum titres of anti-NP IgG1 in individual mice (n=4 for each group) were measured. Data shown are representative from two independent experiments.