CD27+ memory cells				CD27− memory cells
	Switched IgG+/ IgA+/IgE+	Switched IgD+IgM−	IgM memory		FCRL4+	IgG+	IgA+
			IgM-only	IgM+IgD+
Origin	Late GC	Late GC	Early GC	Early GC GC-independent	Not known	Early GC	GC-independent
Tissue distribution	Second lymphoid, PB	Mucosal tissue, PB	Second lymphoid, PB	Second lymphoid (MZ of spleen), PB	MALT	Second lymphoid, PB	PB, gut?
Function	TD response	TD/TI response	TD response?	TI response	Not known	TD response?	TI response?
	TI response?	Basophil activation		TD response?
Transcription factor	RUNX1	Not known	Not known	Notch2?	RUNX2, SOX5	RUNX1?	Not known
% of PB B cells	11–17	1–3	5	15	<0.2% in PB (9.5% in tonsil)	1–4	4