Dendritic cells enhance the differentiation of naive B cells into plasma cells in vitro

We have shown previously that in vitro-generated human dendritic cells have an effect on the response of B cells at various stages of their differenti ation. In a culture system described for the in vitro induction of plasma-c ell differentiation, it was reported that naive B cells have a poor propens ity to differentiate into plasma cells. In such a culture system, 12% of na ive B cells differentiated into plasma cells in the presence of IL-2 and IL -10, despite the interruption of CD40 signalling which is necessary for pla sma-cell differentiation. However, as reported herein, naive B cells differ entiated fully into plasma cells in response to dendritic cells. Addition o f dendritic cells enhanced this differentiation strikingly by recruiting 57 % of B cells as plasma cells producing IgM, but also IgG and IgA. In this m odel, dendritic cells act in synergy with IL-2 at an early stage of CD40-de pendent B-cell differentiation, while IL-2 and IL-10 act together, at a lat er stage, in the generation of plasma cells in a CD40-independent manner. T hus, in addition to the key role played by dendritic cells in the initiatio n of T-cell responses, our results suggest that dendritic cells regulate hu moral responses.