Abstract
Platelets are under investigation for their role in host defence and inflammatory lung diseases and have been demonstrated to be recruited to the lung. However, the mechanisms and consequences of platelet recruitment into lungs are poorly understood. We have utilised a murine model to investigate the mechanisms of platelet involvement in lung inflammation induced by intranasal administration of LPS. Our aim was to characterise lung platelet recruitment following LPS inhalation in mice using immunohistochemistry, and non-invasive and invasive radiolabelled platelet tracking techniques. Intranasal administration of LPS caused an increase in lung platelet staining in lung tissue and elicited the recruitment of radiolabelled platelets into the lung. Prior to these responses in the lung, we observed an earlier decrease in blood platelet counts, temporally associated with platelet recruitment to the liver and spleen. Non-invasive measurements of thoracic radioactivity reflected changes in blood counts rather than extravascular lung platelet recruitment. However, both in situ counting of radiolabelled platelets and immunostaining for platelet surface markers showed LPS-induced increases in extravascular platelets into lung airspaces suggesting that some of the platelets recruited to the lung enter air spaces. Intranasal administration of LPS activates the innate immune response which includes a fall in peripheral blood platelet counts with subsequent platelet recruitment to the lung, spleen and liver, measured by immunohistochemistry and radiolabelling techniques.
Highlights
Mice were administered LPS or PBS intranasally, and blood and lungs were collected 4 h and 48 h afterwards for immunohistochemical analysis of platelets (Fig. 1A & B). Mice subjected to this protocol were transfused with 111In-labelled platelets detected non-invasively using a gamma radiation probe. 48 h after LPS exposure, a time point when lung platelet recruitment was reported to occur in a previous study (Ortiz-Muñoz et al, 2014), increases in both lung platelet staining (Fig. 1C), and lung radiolabelled platelet recruitment were detected (Fig. 1E)
Intranasal LPS administration initially elicited a fall in platelet counts in the peripheral circulation, as measured by serial blood microsampling (Fig. 1D), and the quantity of radiolabelled platelets remaining in blood at 4 h after intranasal challenge (Fig. 1E)
By 48 h following intranasal challenge, there was no significant difference in blood platelet counts (Fig. 1D) or in the retention of radiolabelled platelets in blood between LPS treated mice and PBS controls (Fig. 1F), providing evidence that increases in lung platelet staining were not because of increased circulating platelet counts, and increases in the lung:blood ratio were unlikely due to decreases in blood platelet retention
Summary
Platelets make important contributions to haemostasis, thrombosis, inflammation and regeneration, and drugs targeting platelets have garnered interest as potential anti-inflammatory interventions for the treatment of inflammatory lung diseases (Amison, Arnold, O'Shaughnessy, et al, 2017; Amison, Momi, Morris, et al, 2015; Li, Zarbock, & Hidalgo, 2017; Middleton, Weyrich, & Zimmerman, 2016; Nachman & Weksler, 1972; Page, 1988; Pitchford, 2006; Semple, Italiano, & Freedman, 2011; Weyrich & Zimmerman, 2013). Platelets have been suggested to migrate out of the bloodstream and into tissue and airspaces in inflamed lungs in mouse models of allergic airway inflammation (Pitchford et al, 2008) and following LPS inhalation (Ortiz-Muñoz et al, 2014; Rylander, Beijer, Lantz, Burrell, & Sedivy, 1988), a phenomenon with poorly understood mechanisms and consequences
Sign-in/Register to view highlights & summary 
Published Version (
Free)
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 call