CD27 and activated PI3K-delta syndrome: For both types of APDS patients, peripheral blood (PB) immunophenotyping of B lymphocyte subsets indicated an increased frequency of transitional B cells (CD19+Ig(M)D+CD38+CD24+CD27– or CD20+CD10+CD27-), a reduced frequency of naïve B cells (IgM/IgD+CD27–) and of switched memory B cells (IgD–CD27+), contrasting with an increased frequency of plasmablasts [CD38++CD27++ or CD24-CD38++(IgD-CD27++sIgM-cIgM+)] compared to controls (27, 29, 53, 58).