Regulation of the expression of CD300a on human B cells. (A) Purified naive B cells were activated and cultured according to the protocol described in “Cell cultures.” The expression of CD27, CD300a, and CD305 was assessed at day 0 and day 7 of the cultures. Results are representative of 3 independent experiments. (B) Memory CD27⁺ B cells were purified and sorted according to the protocol described in “Cell cultures” and “Flow cytometric analyses” and stimulated with CpG 2006 for 5 days. Dot plots of IgD and CD27 expression at day 0 (before sorting) and day 5, and a histogram of CD38 expression for a representative culture is also shown (upper panels). Histogram of CD300a expression in the CD27⁺ and CD27⁺⁺ cells and graphic representation of the average relative MFI ± SEM of CD300a expression (n = 4) (lower panels). (C) Purified B cells were stimulated with anti-IgG in the presence of IL-4 or TGF-β1 for 4 days according to the protocol described in “Cell cultures.” Flow cytometric analyses were performed to assess CD300a expression by the CD27⁺ cells. Histograms from a representative donor are shown (left panel) along with the graphic representation of the average relative MFI plus or minus SEM of CD300a expression (n = 4; right panel).