Figure 1: Flow cytometric analysis of B cell sub-populations After gating on lymphocytes according to forward (FSC) and side (SSC) scatter B cells were selected by CD19 surface staining. B cells were then analysed for CD27 and IgD expression to assess the percentage of IgD+ CD27- B cells (1), IgD+ CD27+ B cells (2) and IgD-CD27+ B cells (3). In addition, CD27+ and CD27- B cells were selected and further assessed for surface IgD and IgM staining to determine the percentages of IgD+IgM+CD27+ unswitched memory B cells (4), IgD-IgM-CD27+ class switched memory B cells (5) and IgD+IgM+CD27- naive B cells (6). B cells were further analysed for CD21 and CD38 surface expression to identify CD38loCD21lo B cells (7). In addition, B cells were analysed for IgM and CD38 surface expression to identify CD38+++IgMhi transitional B cells (8) and CD38+++IgM-plasmablasts (9).