The MAPK-signaling pathway is upregulated in COVID-19 ICU patient platelets. (A) Washed platelets were stimulated with 2MeSADP (1 ng/mL), thrombin (0.05 U/mL), collagen (2 μg/mL), or vehicle under stirring conditions for 5 minutes. Platelet proteins were separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), subsequent western blots were probed for phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) (T202/Y204), phosphorylated p38 (T180/Y182), and phosphorylated eIF4E (Ser209). β-actin was used as loading control. (B) Quantification of phosphorylation normalized to β-actin (n = 4). (C) Washed platelets were stimulated with 2MeSADP (1 ng/mL), thrombin (0.05 U), collagen (2 μg/mL), or vehicle under stirring conditions for 5 minutes. Platelet proteins were separated by SDS-PAGE, subsequent western blots were probed for phosphorylated cytosolic phospholipase A2 (cPLA2) (Ser505). (D) Quantification of phosphorylation normalized to β-actin (n = 4). (E) Thromboxane B2 (TXB2) generation was measured as described in “Methods” (n = 8). *P < .05; **P < .01.