Table I.

Summary of the functional and phenotypic heterogeneity evident of mouse memory B cells. Because memory B cells are quiescent, their characteristics are juxtaposed with those of naïve B cells. The PD-L2 and CD80 nomenclature is a new addition to the memory B cell cannon and not all parameters have been determined yet.

	naïve	Heterogeneity in B cell memory
		Memory B cells				Switched or Unswitched Memory B Cells
	IgM	IgM+	IgG+	IgA+	LLPC	PD-L2loCD80lo	PD-L2hiCD80hi
developmental route	n.d.	pre- & post-GC	pre- & post-GC	post-GC	post-GC	not known	not known
tissue tropism	recirculating	recirculating	recirculating	Mucosal	bone marrow and mucosal	not known	not known
S0HM	none	low or high	low or high	high	low or high	low	high
life span	brief	indefinite	decays	not known	indefinite	indefinite	indefinite
propensity for effector cell fates	germinal center ≫ plasma cell	limited by presence of high affinity antibody	plasma cell ≫ germinal center	plasma cell ≫ germinal center	Inert	germinal center ≫ plasma cell	plasma cell ≫ germinal center
repertoire	broad/low affinity	archival?	broad/low affinity	unknown	narrow/high affinity	broad/low affinity	not known
CD19 expression	high	high	high	high	low/absent	high	high
CD20 expression	high	high	high	high	low/absent	high	high
BAFFR expression	high	high	high	high	high	high	high
BCMA expression	low/absent	low/absent	low/absent	low/absent	high	low/absent	low/absent
Potential therapeutics	Alemtuzumab Rituximab	Belimumab Atacicept Rituximab	Belimumab Atacicept Rituximab	Belimumab Atacicept Rituximab	Bortezomib Atacicept IVIG Plasmaphoresis	Belimumab Atacicept Rituximab	Belimumab Atacicept Rituximab