Imaging the unforeseen fate of neutrophils: Inflammation that results from insults such as ischemia and reperfusion or trauma in the absence of microorganisms is known as “sterile inflammation.” Neutrophils are recruited in vast numbers during sterile inflammation and have been thought to play a detrimental role. Wang et al. used intravital microscopy to show that neutrophils actually perform helpful tasks such as removing and regenerating thermally damaged blood vessels in the liver (see the Perspective by Garner and de Visser). Moreover, neutrophils neither die nor are phagocytosed. Instead, they return to the circulation in a process called “reverse transmigration,” making a pit stop in the lungs, before ending their lives where they began—in the bone marrow. Thus, a reconsideration of the use of anti-neutrophil therapies after injury may be warranted. Science , this issue p. 111 ; see also p. 42

Macrophages seal 'em in the coelom: GATA6 ⁺ macrophages resident in body cavities exhibit both phagocytic and repair functions. However, the mechanisms by which these cells can identify and migrate to sites of injury have remained unclear. Using intravital imaging of mouse peritoneal cavities, Zindel et al. report that GATA6 ⁺ macrophages rapidly assemble clot-like structures in a process strongly analogous to thrombosis (see the Perspective by Herrick and Allen). The formation of these aggregates requires the expression of macrophage scavenger receptor domains and acts to plug wounds and promote healing. This pathway can be inadvertently activated during medical procedures, when macrophage aggregates can promote the generation of abdominal scar tissue known as adhesions. Inhibition of macrophage scavenger receptors may therefore be a useful therapeutic approach after surgeries that cause injury to body cavities. Science , this issue p. eabe0595 ; see also p. 993

Background: Nitric oxide (NO) is a multifunctional signaling molecule that regulates important cellular events in inflammation including leukocyte recruitment. Previous studies have shown that pharmacological inhibition of NO synthesis induces leukocyte recruitment in various in vitro and animal models. However, it is not known whether NO modulation has similar effects on leukocyte-endothelial cell interactions within the human microvasculature. The present study explored the effect of systemic L-NAME treatment on leukocyte recruitment in the SCID-hu mouse model. Methods: Human skin xenografts were transplanted in SCID mice to study human leukocyte dynamics in human vasculature. Early events of human leukocyte recruitment in human vasculature were studied using intravital microscopy. NO synthesis was pharmacologically inhibited using N^G-nitro-L-arginine methyl ester (L-NAME). Immunohistochemical analysis was performed to elucidate E-selectin expression in human xenograft skin. Human neutrophil-endothelial cell interactions were also studied in an in vitro flow chamber assay system. P- and E-selectin expression on cultured human umbilical vein endothelial cells (HUVECs) was measured using ELISA. Platelet-activating factor (PAF) synthesis was detected using a TLC-based assay. Results: L-NAME treatment significantly enhanced the rolling and adhesion of human leukocytes to the human vasculature. Functional blocking of P- and E-selectins significantly inhibited rolling but not adhesion induced by inhibition of NO synthesis. Systemic L-NAME treatment enhanced E-selectin expression in human xenograft skin. L-NAME treatment significantly enhanced P- and E-selectin expression on HUVECs. L-NAME treatment did not significantly modify neutrophil rolling or adhesion to HUVECs indicating that L-NAME−induced subtle P- and E-selectin expression was insufficient to elicit dynamic neutrophil-HUVEC interactions in vitro. Moreover, synthesis of endothelial-derived PAF was not significantly modified by L-NAME treatment. These results point to the accelerated leukocyte recruitment in human vasculature following suppression of NO synthesis, effects that are mediated by P- and E-selectins. The findings are, however, not supported by the in vitro data. Conclusion: Inhibition of endogenous NO triggers early events of human leukocyte recruitment in human vasculature, involving complex cellular or molecular mechanisms in addition to P- and E-selectin-mediated leukocyte rolling.

Analgesic Activity of the Different Fractions of the Aerial Parts of Commelina benghalensis Linn

The mechanisms of excessive migration of activated neutrophils into inflamed lungs, credited with tissue damage, are not fully understood. We explored the hitherto unknown expression of leukocyte-specific protein 1 (LSP1) in human and mouse lungs and neutrophils and examined its role in neutrophil migration in acute lung inflammation. Autopsied septic human lungs showed increased LSP1 labeling in epithelium, endothelium, and leukocytes, including in their nuclei compared with normal lungs. We induced acute lung inflammation through intranasal administration of E. coli lipopolysaccharide (LPS) (80 μg) in LSP1-deficient ( Lsp1^−/−) and wild-type (WT) 129/SvJ mice. Immunocytochemistry and Western blots showed increased expression of LSP1 and phosphorylated LSP1 in lungs of LPS-treated WT mice. Histology showed more congestion, inflammation, and Gr-1⁺neutrophils in lung of WT mice than Lsp1^−/−mice. LPS-treated WT mice had significantly more neutrophils in bronchoalveolar lavage (BAL) and myeloperoxidase levels in lungs compared with Lsp1^−/−mice. However, there were no differences in lung tissue and BAL concentrations of keratinocyte-derived chemokine, monocyte chemoattractant protein-1, macrophage inflammatory protein-1α and -1β, vascular permeability, and phosphorylated p38 MAPK between LPS-treated WT and Lsp1^−/−mice, whereas TNF-α concentration was higher in BAL fluid from LPS-treated WT. Immunoelectron microscopy showed increased LSP1 in the nuclei of LPS-treated neutrophils. We also found increased levels of phosphorylated LSP1 associated with plasma membrane, nucleus, and cytosol at various times after LPS treatment of murine bone marrow-derived neutrophils, suggesting its role in modulation of neutrophil cytoskeleton and the membrane. These data collectively show increased expression of LSP1 in inflamed mouse and human lungs and its role in neutrophil recruitment and lung inflammation.