Abstract
Leukocytes circulating in the blood stream leave out of blood vessels and infiltrate into inflamed tissues to perform immune responses. Endothelial cells (ECs) lining interior of the post-capillary venules regulate various steps of leukocyte extravasation. In response to inflammatory signals, ECs upregulate adhesion molecules and produce/present chemokines to support firm adhesion and intraluminal crawling of leukocytes. They also remodel junctions to facilitate leukocyte transendothelial migration (TEM). While roles of apical/lateral components of EC layers in regulating leukocyte extravasation have been extensively investigated, relatively little attention has been paid to the basal part of EC layers comprising subendothelial spaces. In this study, we employed interference reflection microscopy (IRM), a microscopy technique specialized for label-free visualization of cell–substrate contact, to study detailed dynamic interactions between basal part of ECs and T cells underneath EC monolayer. For TEM, T cells on EC monolayer extended protrusions through junctions to explore subendothelial spaces, and EC focal adhesions (EC-FAs) acted as physical barrier for the protrusion. Therefore, preferential TEM occurred through junctions where near-junction focal adhesion (NJ-FA) density of ECs was low. After TEM, T cells performed subendothelial crawling (SEC) with flattened morphology and reduced migration velocity due to tight confinement. T cell SEC mostly occurred through gaps formed in between EC-FAs with minimally breaking EC-FAs. Tumor necrosis factor-α (TNF-α) treatment significantly loosened confinement in subendothelial spaces and reduced NJ-FA density of ECs, thus remodeled basal part of EC layer to facilitate leukocyte extravasation.
Highlights
Circulating blood leukocytes infiltrate into inflamed tissues to eliminate the inflammatory triggers and mediate tissue repair [1, 2]
Leukocyte adhesion cascade is initiated by endothelial cells (ECs) activation by pro-inflammatory cytokines [e.g., tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β)], which results in adhesion molecule upregulation and chemokine production
EC Adhesion–T Cell Interactions performed transendothelial migration (TEM) crawl substantial distances in subendothelial spaces formed between an EC layer and pericytes/basement membrane [subendothelial crawling (SEC)] to breach basement membrane and eventually leave out of blood vessels to infiltrate into inflamed tissues
Summary
Circulating blood leukocytes infiltrate into inflamed tissues to eliminate the inflammatory triggers and mediate tissue repair [1, 2]. Each step of the leukocyte adhesion cascade is regulated by various biochemical/biophysical cues in inflamed blood vessels. Leukocytes sense and response to physical properties of ECs, such as topography [11] and stiffness [12, 13] as well as chemokine gradient [14, 15], to steer directions for ILC, which is a critical step searching for preferential sites in luminal surfaces for TEM. While various factors regulating ILC, including adhesion molecules, chemokines, shear flow, mechanical properties of ECs, has been identified [3, 5, 21], how microenvironments in subendothelial spaces direct SEC has not been completely understood
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
