Background: Long-term outcomes of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are now recognized as an emerging public health challenge - a condition termed post-acute coronavirus 2019 syndrome (PACS) or Long-COVID. The pathophysiology of Long-COVID remains to be established, several mechanisms in study focus on the role of P-selectin, an inflammation-induced protein expressed by platelets and endothelial cells. Functional P-selectin activity, potentially implicated in COVID-19 and Long-COVID sequelae, was measured for a Long-COVID subject at 68 weeks from the SARS-CoV-2 infection after fully recover from the syndrome. It was compared with the results from the same subject at 20 weeks post-infection, when subject experienced severe Long-COVID symptoms. Methods: Flow adhesion of whole blood or isolated white blood cells to P-selectin (FA-WB-Psel and FA-WBC-Psel) was measured using a standardized microfluidics clinical assay; impedance aggregometry with a collagen agonist was measured using model 590 Chrono-Log impedance aggregometer; standard laboratory assays were performed to evaluate changes in blood chemistries. Results: After recovery from Long-COVID, RBC count and D-dimer remained elevated and other blood chemistry results remained within the normal range as compared to 20 weeks post infection when severe Long-COVID symptoms were present. Total iron and transferrin-iron saturation percentage values that were elevated when symptoms were present, declined to normal range. Whole blood aggregometry results indicate an absence of previously present platelet hyperactivity. FA-WB-PSel that was significantly elevated during Long-COVID (590 +/- 260 cells/mm2) was significantly reduced after the resolution of Long-COVID symptoms (98 +/- 38 cells/mm2). However, supplementation of whole blood with crizanlizumab did not result in any measurable inhibition of cell adhesion to P-selectin, similarly with previously reported. Similar to what was observed for the subject when Long-COVID symptoms were present, crizanlizumab, even at a dose 10-fold lower than clinical, induced pronounced inhibition of FA-WBC-Psel when tested in buffer, but not in patient own plasma. Conclusions: This report documents the changes in leukocyte adhesion properties for a patient at more than a year from the initial infection after the gradual resolution of Long-COVID symptoms, as compared to when Long-COVID symptoms were present. Recovery from Long-COVID may be associated with normalization of platelet activity, but not necessarily with complete alleviation of endothelial activation. It remains to be determined to what extent changes in leukocyte adhesion to P-selectin may represent a new risk factor for a mechanism driving Long-COVID syndrome.

M. Ferranti and A. Zaidi are employees, and X. Gao, P. Hines, and M. Tarasev are employees and shareholders of Functional Fluidics Incorporated, a company developing and commercializing assays for assessment of blood cell functions.

This study was internally funded by Functional Fluidics Inc, a company that develops assays for assessment of functional properties of blood cells.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Ethical approval for the study was under the protocols FF-RBC-001 and FF-RBC-003v2 approved by Institutional Review Board of the Institute for Regenerative and Cellular Medicine.

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All data produced in the present study are available upon reasonable request to the authors