The transactivation domain of Spi-B is not required for regulation of plasma cell differentiation. (A) CD34⁺CD1a⁻ progenitors isolated from human postnatal thymus were transduced with control, Spi-B/full-length (fl), or Spi-B/ΔTAD constructs and cultured on OP9 with Flt3L and IL-7. The histogram shows surface expression level of CD40 on CD123⁺BDCA2⁺pDCs transduced with control (shaded histogram), Spi-B/fl (solid line), and Spi-B/ΔTAD (dashed line) constructs. (B) Peripheral blood CD19⁺ B cells were transduced with control, Spi-B/fl, or Spi-B/ΔTAD constructs and cultured in conditions promoting plasma cell differentiation (as in Figure 1). After 7 days of culture, GFP⁺ cells were analyzed for CD19, CD20, CD38, and CD138 surface expression. Contour plots of one representative experiment of 2 are shown. Numbers in the quadrants indicate percentages of cells.