Page 115 - 2021_10-Haematologica-web

Vitronectin stabilizes leukocyte adhesion
less than 30 s was significantly higher in VN-/- mice than in WT controls. Consequently, the average adhesion time of a neutrophil to the microvascular endothelium was sig- nificantly shorter in VN-/- mice than in WT controls. This defect of neutrophils in VN-/- mice to stabilize intravascu- lar adhesion resulted in a significantly reduced number of extravasated neutrophils. Noteworthy, a minority of neu- trophils in VN-/- mice was still able to stabilize their adher- ence to the microvascular endothelium, which might be explained by the heterogeneous expression levels of the VN receptor LRP-1 (Online Supplementary Figure S1)
A
and/or compensatory mechanisms in a subset of these immune cells. Such alternative mechanisms (which might even include cumulative factors) controlling the stabiliza- tion of neutrophil adherence are still unclear and subject of future investigations.
In order to exclude neutrophil-intrinsic effects of VN deficiency on the stabilization of intravascular adhesion of these immune cells, we conducted bone marrow cell transfer experiments (Figure 2B). In the postischemic mouse cremaster muscle (I/R 30/120 min), the number of accumulated fluorescence-labeled neutrophils isolated
B
Figure 1. Role of vitronectin for leukocyte trafficking to inflamed tissue. (A) Using confocal laser scanning microscopy on tissue whole mounts of the cremaster muscle of wil-type (WT) mice, deposition of vitronectin (VN) (green) in the PECAM-1/CD31+ microvasculature (blue) was analyzed, representative images are shown (scale bar: 20 mm). Panels show quantitative results from relative fluorescence intensity measurements for VN in sham-operated WT mice as well as in WT mice undergoing ischemia-reperfusion (I/R) (30/120 min) and intravenous application of glycosaminoglycans digesting enzymes or vehicle (mean±standard error of the mean [SEM] for n=4 animals per group; #P<0.05 vs. sham; *P<0.05 vs. vehicle). (B) Employing multi-channel flow cytometry, the recruitment of neutrophils and classical monocytes to the peritoneal cavity was analyzed 6 hours after intraperitoneal (i.p.) injection of CXCL1 or CCL2, the gating strategy is shown. Panels show results for lipopolysac- charide-treated WT control mice as well as for WT, VN+/-, or VN-/- mice receiving an i.p. injection of CXCL1 or CCL2 (mean±SEM for n=4 animals per group; #P<0.05 vs. control; *P<0.05 vs. WT). cMO: classical monocytes; ncMO: nonclassical monocytes; N: neutrophils; SSC: side scatter.
haematologica | 2021; 106(10)
2643