Background

Although more attention has been paid recently to B-cell immunity, assay for B-cell analysis has yet to be clinically applicable because, unlike T cell, a B-cell culture system has not been well established.

Methods

We attempted to develop an in vitro culture system for the proliferation and differentiation of peripheral B cells into plasma cells, and to analyze the action of everolimus (EVR), mycophenolic acid (MPA), and prednisolone (PRD).

Results

Using a three-step culture system, peripheral CD19+ B cells could differentiate into plasma cells and produce IgG antibody. Activated B cells (CD19 (hi) CD38 (lo) IgD (−)), plasmablasts (CD19 (hi) CD38 (hi) IgD (−)), and plasma cells (CD19 (lo/−) CD38 (hi) IgD (−)) were observed as a main cell subset in step 1 (day 0–4), 2 (day 4–7), and 3 (day 7–10), respectively. IgG production on day 10 was significantly suppressed by EVR, MPA, and PRD, but not cyclosporine. Although both EVR and MPA inhibited B-cell proliferation and differentiation in step 1, EVR suppressed B-cell differentiation in step 2. Only a high concentration of PRD significantly inhibited B-cell proliferation, differentiation, and IgG production in step 3.

Conclusions

Although both MPA and EVR efficiently suppressed cell proliferation during the early phase of B-cell immune reaction, EVR could act in a later phase than MPA. PRD at a high concentration worked even in the last phase. An in vitro B-cell culture system would clarify the mode of drug action during B-cell differentiation and provide useful information on the effective selection or combination of immunosuppressive agents.