Inflammatory Chemokines Direct and Restrict Leukocyte Migration within Live Tissues as Glycan-Bound Gradients

Abstract

Chemokines are essential in many cell migration processes, including the recruitment of leukocytes to sites of infection. In the latter context, chemokines promote leukocyte extravasation into the relevant tissue through a well-studied cascade of events. It is widely believed that chemokines further guide leukocytes within tissues via chemotaxis, the directed migration along gradients of soluble ligands. However, the basic mechanism of chemokine action within tissues has yet to be formally addressed in vivo. We identified a chemokine (zCxcl8) that recruits zebrafish neutrophils to infection loci and analyzed its function directly within interstitial tissues of living larvae. Using noninvasive imaging and a controlled cellular source of zCxcl8, we found that zCxcl8 guides neutrophils in a 2-fold manner: by biasing cell speed according to direction (orthotaxis) and by restricting cell motility near the source. We further show that zCxcl8 establishes tissue-bound gradients in vivo by binding to heparan sulfate proteoglycans (HSPGs). Inhibition of this interaction compromised both directional guidance and restriction of neutrophil motility. Thus, by interacting with extracellular HSPGs, chemokines establish robust surface-bound (haptotactic) gradients that mediate both recruitment and retention of leukocytes at sites of infection.

Gcsf-Chr19 Promotes Neutrophil Migration to Damaged Tissue through Blood Vessels in Zebrafish

“…Although both cytokines Cxcl8 and Gcsf-Chr19 trigger the migration of neutrophils, the first makes it through the interstitial tissue (33) and the second via blood vessels (34). On the other hand, antecedents indicate that the Cxcl8 contribution to neutrophil migration is to attract them to the wound by biasing cell speed according to direction and by restricting cell motility near the source of the chemokine (33). According to these data and the working hypothesis of this paper, Gcsf-Chr19 should control neutrophil output from the CHT toward the blood vessels and Cxcl8, the final migration to the wound through the extracellular matrix.…”

On the move: endocytic trafficking in cell migration

“…Although this concept has been established based on in vitro assays, it is widely accepted. Two recent studies now provide direct evidence from tissues that gradients of the chemokines CXCL8 and CCL21 for attracting leukocytes are established by glycan binding [3,4]. Interestingly, some chemokines such as CCL2 are additionally stored locally in vesicles resembling type 2 granules that are docked on actin fibers just beneath the plasma membrane of endothelial cells, and hence are not exposed at the surface and not visible [5].…”

Immunity and Immunopathology in the Tuberculous Granuloma

“…CCL7 is an appealing candidate because it is a substrate of MMP9 in vivo (Greenlee et al 2006), is produced by macrophages in response to mycobacterial infection (Scott and Flynn 2002), and can recruit monocytes from thebloodstream(SoehnleinandLindbom2010). Other nonmutually exclusive mechanisms could involve remodeling of the extracellular matrix at the site of infection through the release of a sequestered chemoattractant (e.g., glycanbound chemokines) (Sarris et al 2012) or degradation of a physical barrier (e.g., a-dystroglycan proteolysis along basement membranes) (Parks et al 2004;Agrawal et al 2006).…”