Fluid Flow Regulates Stromal Cell Organization and CCL21 Expression in a Tissue-Engineered Lymph Node Microenvironment

Abstract

In the paracortex of the lymph node (LN), T zone fibroblastic reticular cells (TRCs) orchestrate an immune response by guiding lymphocyte migration both physically, by creating three-dimensional (3D) cell networks, and chemically, by secreting the chemokines CCL19 and CCL21 that direct interactions between CCR7-expressing cells, including mature dendritic cells and naive T cells. TRCs also enwrap matrix-based conduits that transport fluid from the subcapsular sinus to high endothelial venules, and fluid flow through the draining LN rapidly increases upon tissue injury or inflammation. To determine whether fluid flow affects TRC organization or function within a 3D network, we regenerated the 3D LN T zone stromal network by culturing murine TRC clones within a macroporous polyurethane scaffold containing type I collagen and Matrigel and applying slow interstitial flow (1–23 μm/min). We show that the 3D environment and slow interstitial flow are important regulators of TRC morphology, organization, and CCL21 secretion. Without flow, CCL21 expression could not be detected. Furthermore, when flow through the LN was blocked in mice in vivo, CCL21 gene expression was down-regulated within 2 h. These results highlight the importance of lymph flow as a homeostatic regulator of constitutive TRC activity and introduce the concept that increased lymph flow may act as an early inflammatory cue to enhance CCL21 expression by TRCs, thereby ensuring efficient immune cell trafficking, lymph sampling, and immune response induction.

Role of Lymphatic Vessels in Tumor Immunity: Passive Conduits or Active Participants?

“…These changes can be observed at very low fluid flows of 0.1-1dyn/cm 2 , which is well-correlated to the slow interstitial flows observed in normal and inflamed tissue. Flow also enhances the expression of CCL21 both in lymphatic vessels [40] and in the lymph node [41]. In addition to activating lymphatic endothelium, lymphatic drainage also facilitates interstitial flow, directed towards the lymphatics.…”

“…Fluid flow through this FRC/collagen network is required for proper 3D organization in vitro [41]. During acute inflammation or injury, lymph flow through the LN can be increased, dramatically enhancing CCL21 expression by FRCs [41] and accelerating the rate of APC and antigen delivery to the draining LN.…”

“…During acute inflammation or injury, lymph flow through the LN can be increased, dramatically enhancing CCL21 expression by FRCs [41] and accelerating the rate of APC and antigen delivery to the draining LN. Occlusion of the afferent lymphatic vessel, and consequent blockage of lymph flow into the LN, results in alterations in high endothelial venules (flattening of lumen and decreased luminal peripheral node addressin expression) and a subsequent decrease in lymphocyte extravasation from the blood [61].…”

“…Second, the lymphatic endothelium itself may express tumor antigen to delete CD8 + effector cells, as it does in the lymph node with endogenous peripheral tissue antigen [8]. Finally, the increased drainage it induces to the draining LN [131][132][133] could activate the tolerance-maintaining functions of the lymph node by upregulating CCL21 [41] and bathing the LN with tumor antigen.…”

Alterations in maternal and fetal heart functions accompany failed spiral arterial remodeling in pregnant mice

“…17,18 This indicates that gains in uterine flow are more attributable to morphological remodeling of uterine arteries than to alterations in their smooth muscle tone. 19 Mouse models have promoted understanding of mechanisms regulating gestational changes to the cardiovascular system. 20 Comparisons of micro-ultrasound measurements of placental growth and blood flow velocity between normal and mutant mice (i.e.…”