Frequencies and absolute numbers of B cell subsets. Frequencies and numbers of CD27-IgD+CD38++ transitional (A) and CD27-IgD+CD38+ naïve B cells (B) were significantly lower in patients taking azathioprine (AZA) compared to mycophenolate mofetil (MMF)-treated patients or patients not taking immunosuppressive therapy (no IS). Absolute numbers of CD27+IgD+ pre-switched memory B cells (C) were significantly lower in patients taking AZA compared to patients without IS. However, absolute numbers of CD27+IgD- post-switched memory B cells did not differ significantly (D). Patients taking AZA had the highest, and patients taking MMF the lowest frequency of CD27+IgD- post-switched memory B cells (D). Median values are shown: statistically significant differences were detected comparing patients on AZA and MMF (*P < 0.05, **P < 0.01, ***P < 0.001) or patients on AZA (§P < 0.5, §§P < 0.01, §§§P < 0.001) or patients on MMF (#P < 0.05, ##P < 0.01, ###P < 0.001) to patients without immunosuppressive therapy (Dunn's multiple comparison test).