Lymph node B lymphocyte trafficking is constrained by anatomy and highly dependent upon chemoattractant desensitization

Abstract

IntroductionLymphocyte homeostasis in resting lymph nodes (LNs) is maintained by the entry of circulating lymphocytes through high endothelial venules (HEVs) and exit through lymphatic vessels. CD62L on lymphocytes interacts with ligands on HEVs in LNs to initiate the rolling of lymphocytes along the luminal surface. 1,2 As the lymphocytes roll, cognate G-protein coupled receptors (GPCRs) engage homeostatic chemokines present on the luminal surface of HEVs triggering lymphocyte adhesion and the exploration for a transendothelial migration (TEM) site. 3 After penetrating the endothelial basement membrane, the cells negotiate the perivenule space to emerge in the paracortical cords (PCCs). [4][5][6] These cords originate between and below LN follicles and extend to the medullary region of the LNs where they merge with the medullary cords. After crossing the HEVs, the migratory paths of B and T lymphocytes diverge. T cells migrate along CCL19/21 expressing fibroreticular cells (FRCs) using their prominently expressed CCR7 to access the LN deep cortex whereas B cells rely on their prominent CXCR5 expression to access the LN follicle. [7][8][9] Newly resident B cells tend toward the follicle centers, sites of high CXCL13 expression, whereas long-term LN follicle residents move toward the edges closer to egress sites. 10 To enter the efferent lymph in route to the blood, B cells must leave the LN follicle, and eventually traverse the efferent lymphatic endothelium.Although the high concentration of chemokines in the LN opposes lymphocyte LN egress, 11 another GPCR the sphingosine-1 phosphate receptor 1 (S1P1 receptor) has been implicated in facilitating lymphocyte egress into the lymph. [12][13][14] The LN parenchyma, although rich in homeostatic chemokines, has little S1P whereas the lymph and blood have high levels. A delicate balance between the synthesis, transport, and degradation of S1P achieves and maintains this gradient. 15 An explosion of interest in S1P signaling followed the observation that the administration of a S1P analog FTY720 caused lymphopenia by preventing lymphocyte LN egress. 12 Despite intensive scrutiny, a consensus on the mechanism by which FTY720 causes lymphocyte retention hasn't emerged. 13,16 However, a recent study has implicated lymphocyte S1P1 receptor cell-surface residency as a crucial factor in lymphocyte egress kinetics after FTY720 treatment. 17 Less controversy surrounds the concept that the lymphocyte S1P1 receptor functions to facilitate normal lymphocyte LN egress, although the precise mechanism by which it does so remains unresolved. 10,18 In this study, we used a combination of immunohistochemistry, intravital microscopy, and in vitro chemotaxis assays to study the trafficking of B cells through the inguinal LNs of mice. Based on our results, we offer a model of homeostatic B-cell trafficking through LNs. Methods Mice and cellsC57BL/6, B6.129P2(C)-Ccr7 tm1Rfor/JϪ , and B6.SJL-Ptprc a Pepc b /BoyJ mice were obtained from The Jackson Laboratory. Gnai2 Ϫ/Ϫ mice 19 were provided...

Naive B-cell trafficking is shaped by local chemokine availability and LFA-1–independent stromal interactions

“…This is similar to observations made by Park and colleagues. 5 This may be due to one or several of the following scenarios: subsets of stromal cells in the T-cell area express CXCL13, 38 which may present low levels of CXCL13 in the T-cell area, thereby disrupting a chemotactic gradient. However, in immunofluorescent sections, virtually all detectable CXCL13 is found in B-cell follicles.…”

“…The labeling for HEV allowed us to discard tracks in the perivascular space where migration is lower than in the parenchyma. 3,5 While the track distribution analysis confirmed that CXCR5 was required for efficient entry into the follicular microenvironment, CXCR5…”

“…B cells express CCR7 23 and show a strong chemotactic response in vitro to CCL21 (Figure 2A), which promotes LFA-1 activation in HEV. 1,5 Similarly, B cells respond to CXCL12 with strong migration, which can be blocked by the CXCR4 antagonist NIBR1816 ( Figure 2B). 22 We first determined whether CCR7 propels B cells within the T-cell area and retains B cells in this microenvironment, thereby inhibiting random entry of CXCR5 2/2 B cells into follicles.…”

“…Male and female 8-to 12-week-old CXCR5 2/2 mice, 4,5,8 plt/plt mice, 6,7,18 CCR7 2/2 mice, [8][9][10]19 and ICAM-1-deficient mice [11][12][13][14]20 on the C57BL/6 background were bred at our animal facility (Bern, Switzerland); Ebi2 2/2 mice (C57BL/6 strain) and CH25H 2/2 mice 3,21 on the C57BL/6 background were bred at Novartis (Basel, Switzerland). Sex-and age-matched C57BL/6 mice (Harlan, the Netherlands) were used as wild-type lymphocyte donor or recipient mice.…”

“…[1][2][3] Studies in mice have shown that B cells accumulate from their entry point in the T-cell area in 1 of approximately 7-35 B-cell follicles located in the peripheral lymph node (PLN) cortex. 4,5 During their migration inside lymphoid tissue, B cells use the ICAM-1-expressing fibroblastic reticular cell (FRC) network of the T-cell area and the follicular dendritic cell (FDC) network in follicles as guidance structures. 6,7 Analysis of tissue sections has shown that B-cell accumulation inside follicles is critically dependent on CXCR5 and CXCL13 production by FDCs.…”