Interleukin-6 is a growth factor for nonmalignant human plasmablasts

Abstract

Interleukin-6 (IL-6), although often regarded as a B-cell differentiation factor, was recently described as the essential survival factor for human plasmablasts in vivo in reactive plasmacytosis. The present study reinvestigated the roles of IL-6 and IL-2 in the generation of plasma cells from human memory B cells in vitro. The cells involved in this differentiation process were identified as preplasmablasts (CD20±CD38±CD138−), plasmablasts (CD20−CD38++CD138−), and early plasma cells (CD20−CD38+++CD138+++). IL-2 or IL-10 induced a strong generation of plasmablasts and early plasma cells (PCs). Compared to IL-2 or IL-10, IL-6 alone was inefficient at PC generation. However, when combined with IL-2 or IL-10, IL-6 enhanced generation of early PCs. Moreover, anti–IL-6 monoclonal antibody markedly reduced IL-2–induced generation of early plasma cells, but not of plasmablasts. These roles of IL-2 and IL-6 were consistent with the difference in the expression of their respective receptors (R). CD25 (IL-2Rα) was increased 72 ± 10-fold on activated B cells, but decreased and then disappeared on plasmablasts. Conversely, CD126 (IL-6Rα) was barely expressed on activated B cells, but increased 18 ± 2-fold on preplasmablasts. Finally, IL-6 enhanced the proliferation (2-fold increase) of IL-2–generated plasmablasts. In conclusion, the data indicate that IL-6 is a growth factor for nonmalignant human plasmablasts.