Cytokine expression and regulation of human plasma cells: disappearance of interleukin‐10 and persistence of transforming growth factor‐β1

Abstract

Less is known about the cytokine expression and regulation of normal plasma cells compared to that of activated B cells or myeloma cells. This study shows that nonproliferating (hydroxyurea‐treated), immunoglobulin (Ig)‐secreting cells generated from human B cells in the EL‐4 culture system no longer express interleukin (IL)‐6 mRNA, progressively lose IL‐10 mRNA, but continue to express transforming growth factor (TGF)‐β₁ mRNA. Secretion of TGF‐β₁ protein was demonstrated. On the other hand, and in contrast to the suppression of B cell proliferation and Ig secretion, the basal or the IL‐6/IL‐10 stimulated Ig secretion of nonproliferating cells was not inhibited by recombinant TGF‐γ₁. Plasma cells isolated from human bone marrow expressed neither IL‐6 nor IL‐10 mRNA; only TGF‐β₁ mRNA was detected by reverse transcription–polymerase chain reaction analysis. Such plasma cells may be on average more “aged” cells than those generated in vitro. Thus, plasma cells persistently express TGF‐β₁, a known suppressor of various lymphoid and hemopoietic cell activities, but do not limit their own Ig secretion via this cytokine.