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Coronavirus Disease 2019 (COVID-19) has been widely associated with increased thrombotic risk, with many different proposed mechanisms. One such mechanism is acquired deficiency of protein S (PS), a plasma protein that regulates coagulation and inflammatory processes, including complement activation and efferocytosis. Acquired PS deficiency is common in patients with severe viral infections and has been reported in multiple studies of COVID-19. This deficiency may be caused by consumption, degradation, or clearance of the protein, by decreased synthesis, or by binding of PS to other plasma proteins, which block its anticoagulant activity. Here, we review the functions of PS, the evidence of acquired PS deficiency in COVID-19 patients, the potential mechanisms of PS deficiency, and the evidence that those mechanisms may be occurring in COVID-19. [ABSTRACT FROM AUTHOR]

Abstract: Aims: To study protein S, as an acute phase protein, for its relationships with C4b-BP (C4BP), fibrinogen and Factor VIII:C in a group of patients with solid tumours, without proven metastases. Methods: Eighty-one consecutive patients with gastrointestinal or pelvic adenocarcinoma (TNM staging: T1-3, N0-2, M0) and 58 healthy subjects were evaluated for plasma free and total protein S antigen, protein S activity, C4BP, fibrinogen and Factor VIII:C. Results: When compared to the control group, the total protein S, the C4BP, the fibrinogen and the Factor VIII:C mean levels were significantly higher in the cancer group, but there was no significant difference for the free and the functional protein S mean concentrations. In both groups the free protein S was correlated with the functional and the total protein S; moreover the latter was significantly correlated with the C4BP, whereas it was significantly correlated with the fibrinogen and the Factor VIII:C only in the cancer group. In addition, a high correlation was found among the C4BP, the fibrinogen and the Factor VIII:C. Conclusions: Our data show that in these patients there is an acute phase response and suggest that, in the thrombophilic early cancer screening, determination of free protein S is redundant. [Copyright &y& Elsevier]