MPA inhibited all non-PC subpopulations of B cells isolated from both the peripheral blood and tonsil. A, Naive and preswitched and postswitched memory B cells were isolated from peripheral blood. Data represent three independent experiments. B, Naive, memory, and GC B cells were isolated from the tonsil. Cells were stimulated with either IL-21, anti-CD40, and anti-IgM or CpG-B in the presence of DMSO control or MPA at the indicated concentrations. ATP units were quantified on day 3. Data represent three independent experiments. Mean and SD of triplicate wells is shown where possible. For IgM+ memory B cells (A) and GC B cells (B), the average of duplicate wells is shown.