Table 1 Summary of main phenotypic and functional characteristics of B-cell subsets

Marginal Zone B-cells

SIgM^hi SIgD^loCD27+ CD21^hi

Mutated BcR in humans on >80% MZ B-cells

67-69,72

CD23-

TI-Ab response. Produced Low affinity IgM

CD21 modulates BCR signalling

141

CXCR5+ S1P1^hi S1P3^hi

Preferential sequestration in MZ, shutling into follicles upon stimulation

55, 56, 58, 59

BcR-independent transport of high MW Ags and virus particles into GC

56,83

Present in periphery (blood, Lymph node, spleen) in humans

69

TLR 2> 1, 6; TLR10

Surface TLRs associated into functional TLR2/1 or TLR2/6 complexes

108, 109

TLR9>7

Endosomal TLR detecting unmethylated CpG DNA and ssRNA

CD1c^hi

Expression ↘ upon CD40L stimulation but ↗ after BcR triggering

115

LDL-R+

Binds and internalizes lipid Ags associated with Apo-E

117

CD1d^hi

Presents lipid Ags to iNKT

116, 119-122

CD1d expression decreases rapidly after BCR or CD40 activation

118

Cognate interactions with iNKT, which in turn produce IL17 and IL22

119-122

BAFF-R++, TACI+

Strong expression of their ligand, BAFF, in MZ. Survival of MZ B-cells.

75

Role of BAFF in the transient relocalisation of MZ B-cells into follicles

Follicular Naive B-cells

SIgM+ SIgD^hiCD27- CD21+CD23^hi

Unmutated BcR.

CXCR5++ S1P1+ S1P3-

Preferential homing to follicles

56

TLR 2> 1, 6, TLR10

Surface TLRs associated into functional TLR2/1 or TLR2/6 complexes

108,109

TLR9>7

Endosomal TLR detecting unmethylated CpG DNA and ssRNA,

CD1c+, CD1d^hi

Functional role?

118

BAFF-R++, TACI+

Naive B-cell survival

Conventional Memory B-cells

SIgD-, SIgG/A>SIgM, CD27+

High affinity hypermutated BcR

CD21^hiCD23-

Role of CD21 in memory B-cell survival

141

TLR9++, TLR7+

↗ expression of TLR 7, 9 in memory B-cells compared to naive B-cells

7,113

BAFF-R+TACI+

BAFF preferentially enhances memory B-cell chemotaxis to CXCL13

86

Regulatory B-cells

CD1d^hi CD5+ TIM-1+

B10:IL10-producing B-cells in mice. Located in/near MZ

123,124

Expanded by BAFF in mice

130

CD27+

IL10-producing memory B-cells in humans

127, 132-134

CD19+CD24^hi CD38^hi

IL10-producing transitional B-cells in humans. Regulatory functions on CD4+ T-cells

134

CD21 ^lo/- B-cells

CD19+ SIgM+ BAFF-R+ CD21-

No response to BcR, CD40 or BAFF-R stimulation

134

CD23-CD43-

Production of IgM, IL10 and IL4 in response to TLR9, 7 stimulation

Induce IL17 production by activated T-cells

115

CD21^lo CD11c+ CD5+ CD138+

Present in aged and autoimmune mice. Pre-plasmablasts?

157

CD95^hi CD80^hi CD86^hi

No response to BcR stimulation but produced IgG after TLR7 triggering

CD20^hi CD21^lo CD11c+ CD5^hiCD27^hi

Present in blood of elderly female autoimmune patients

132,133

CD23-SIg-CD80^hiCD86^hi

Pre-plasmablasts?

CD21^loCD27+

Activated B-cells or pre-plasmablasts present in HIV-infected patients

148-150

CD21^loCD27-PD1+ FcRL4+

Exhausted tissue-like memory B-cells present in HIV-infected patients

148-150