In vitro plasmablast and plasma cell differentiation increases B-cell IL-10 production. Purified B cells from a healthy donor were cultured for 4 days with crosslinked recombinant human CD40L, CpG-B, IL-2, IL-10, and IL-15, followed by a 3-day culture with IL-2, IL-6, IL-10, and IL-15 and a 3-day plasma cell differentiation with IL-6, IL-15, and IFN-α as described.⁴¹  B-cell surface phenotypes (on freshly harvested cells) and intracellular IL-10 (after 5-hour PMA + ionomycin stimulation) were assessed by flow cytometry at days 1, 4, 7, and 10. Data are representative of 3 experiments. (A) Histograms of the expression of CD27, CD38, and CD138 by cultured B cells at days 1, 4, 7, and 10 (top panels). CD19⁺IL-10⁺ cells in proportion to total live CD19⁺ cells at the corresponding time points (bottom panel). (B) B-cell phenotypes and morphology (after May-Grünwald-Giemsa staining of the cytospinned cells) and IL-10 production by the expanded CD27^hiCD38^hiCD138⁺ B-cell pool at day 10. (C) CD19⁺IL-10⁺ cells as determined by flow cytometry in proportion of live CD19⁺ at days 1, 4, 7, and 10 in 3 independent experiments.