Figure 7: IL-21 promotes differentiation of iGB cells towards plasma cells.

(a) The frequency of NP-specific IgG1 AFCs among BM cells determined by ELISPOT assay. Shown is collective data with averages (bars) from five experiments using individual mice that had received iGB-4 (n=4), iGB-21 (n=3), or iGB-m (n=5) CD138⁻ IgG1⁺ NP⁺ iGB cells derived from B1-8 ki mice 26–30 days before. Photographs depict representative ELISPOT wells seeded with 5×10⁵ total BM cells. (b) Quantitative real-time PCR analysis of Blimp-1 transcripts in the following cells: splenic follicular B cells (CD43⁻, CD138⁻, CD19⁺, CD23^high, CD21⁺) sorted from unimmunized C57BL/6 mice, physiological GC B cells (CD43⁻, CD138⁻, IgD⁻, CD19⁺, Fas⁺, GL7⁺) sorted from C57BL/6 mice immunized with BSA/CFA 3 weeks before, CD138⁻ IgG1⁺ cells sorted from iGB-4, iGB-21 or iGB-m cells, and CD138⁺ cells from iGB-21 or iGB-m cells, each collected on the indicated day of the culture. Expression levels relative to that in follicular B cells (set as 1) are shown. Data is representative of two independent experiments. Error bars represent s.d. of triplicate samples. (c) CD138⁺ or CD138⁻ and IgG1⁺ cells were purified by MACS from iGB-4 and iGB-21 cells on day 6 or iGB-21 and iGB-m cells on day 8, and the frequency of anti-NP IgG1⁺ AFCs in these cells and pre-purified total IgG1⁺ cells was determined by ELISPOT. iGB-4, iGB-21 and iGB-m cells are shown as black, grey and white bars, respectively. Data is representative of two independent experiments.