Fig 2: Overall summary of the study. Seventy-five participants diagnosed with COVID-19 via detection of SARS-CoV-2 using a PCR test were divided into Mild, Moderate, and Severe groups based on total number of liters of oxygen utilized during acute infection. Blood plasma and platelets were isolated from blood samples taken between July 2020 and April 2021. Cytokine profiling and protein analysis of plasma samples were performed using a 10-plex immunothrombotic ELISA-type assay and proteomics, respectively. Participants with elevated Factor IX, P-selectin, and tPA, in addition to low D-dimer and activated platelets were more likely to develop Post-Acute Sequelae of COVID-19 (PASC) at least 60 days after infection. NET: neutrophil extracellular traps; tPA: tissue-type plasminogen activator; PSGL-1: P-selectin glycoprotein ligand-1; PCR: polymerase chain reaction

Fig 3: Plasma biomarker levels in patients with and without PASC. This figure illustrates the plasma concentrations (pg/mL, log10 scale) of various biomarkers, including D-Dimer, Factor IX, IL-6, IL-8, P-selectin, plasminogen activator inhibitor -1 (PAI-1), P-selectin glycoprotein ligand-1 (PSGL-1), sCD40L, Tissue Factor, and tissue-type plasminogen activator (tPA), stratified by Post-Acute Sequelae of COVID-19 (PASC) status (No PASC in black and PASC in red) over three time intervals post-disease onset (1–35 days, 36–76 days, and >77 days). The data reveal distinct patterns, with elevated levels of Factor IX, Tissue Factor, and tPA elevated in the early stages of disease (1–35 days) among patients who eventually go on to develop PASC. These findings suggest a potential link between these biomarkers and the development or persistence of PASC, providing insight into the underlying pathophysiology and potential targets for monitoring or intervention

Fig 4: Persistent platelet activation in individuals with PASC. Flow cytometry analysis of whole blood was performed to assess platelet activation in individuals with and without Post- Acute Sequelae of COVID-19 (PASC). Platelets were stained for CD41 (integrin αIIb), CD62P (P-selectin), and PAC1 (Procaspase-activating compound 1). The frequency of CD41⁺CD62P⁺PAC1⁺ platelets was quantified using FlowJo. Data are displayed as jitter plots overlaid with boxplots, with the y-axis showing the percentage of total CD41⁺CD62P⁺PAC1⁺ cells out of total stained blood cells. Statistical comparison between groups was performed using the two-tailed Mann-Whitney U test. The graph was plotted using R, version 4.3.1