Evidence of abortive plasma cell differentiation in Hodgkin and Reed‐Sternberg cells of classical Hodgkin lymphoma

Abstract

Hodgkin and Reed‐Sternberg (HRS) cells of classical Hodgkin lymphoma (cHL) show genotypic features of germinal centre‐derived B‐cells in most cases. Nevertheless, these cells typically lack expression of B‐cell antigens. Previous studies have suggested that plasma cell differentiation may occur in HRS cells and that this may account for the down‐regulation of B‐cell antigens. However, these results are controversial. We have addressed this question using immunohistochemistry and a panel of antibodies directed against antigens which are differentially expressed during terminal B‐cell differentiation. Pax‐5, a transcription factor required for B‐lineage commitment, and IRF4/Mum1, which is physiologically expressed in germinal centre cells and plasma cells, were consistently detectable in HRS cells. Bcl‐6, a transcription factor expressed in germinal centre B‐cells, was present in HRS cells of approximately 25% of cHL cases. Expression of the B‐lymphocyte‐induced maturation protein‐1 (Blimp‐1), a key regulator of plasma cell differentiation, was observed in HRS cells of 23% of cHL cases. In these cases, Blimp‐1 expression was restricted to a small proportion of HRS cells. HRS cells were consistently negative for the plasma cell marker CD138. These results suggest that plasma cell differentiation may be initiated in a small subset of HRS cells but remains abortive. Thus, terminal differentiation is unlikely to explain the lack of B‐cell antigen expression in HRS cells. Copyright © 2005 John Wiley & Sons, Ltd.