Fig 1: Histological staining and quantification of stroke thrombi. a Representative adjacent thrombus slides stained with Martius Scarlet Blue (MSB, left superior) and immunostained for platelets (CD42b), S100A9, and neutrophil elastase (in brown). b Magnifications of the area selected in panel a. MSB staining shows a red blood-rich area (orange-yellow, arrowhead) near to a collagen area (light blue, arrow). A fibrin area at the periphery appears in red (asterisk). Platelet-rich regions (CD42b staining in brown) are related with collagen areas. Neutrophil elastase (brown) tends to accumulate at the boundary of platelet-rich zones (brown with CD42b staining) and S100A9 distribution seems to be related with neutrophil and monocyte (neutrophil elastase +) presence at the interface between red blood cell-rich and platelet-rich areas and also within platelet islets. c Box-plot showing the differences in percentage of S100A9 staining in thrombi retrieved from cardioembolic and atherothrombotic stroke patients. Calculated by Wilcoxon rank-sum test. d Box-plot showing the differences of S100A9 percentage in thrombi from patients who died or survived after stroke. Calculated by Student t test over log-transformed S100A9