Mannose-Binding Lectin is Associated with Thrombosis and Coagulopathy in Critically Ill COVID-19 Patients

Abstract

The ongoing COVID-19 pandemic has caused significant morbidity and mortality worldwide, as well as profound effects on society. COVID-19 patients have an increased risk of thromboembolic (TE) complications, which develop despite pharmacological thromboprophylaxis. The mechanism behind COVID-19-associated coagulopathy remains unclear. Mannose-binding lectin (MBL), a pattern recognition molecule that initiates the lectin pathway of complement activation, has been suggested as a potential amplifier of blood coagulation during thromboinflammation. Here we describe data from a cohort of critically ill COVID-19 patients (n = 65) treated at a tertiary hospital center intensive care unit (ICU). A subset of patients had strongly elevated MBL plasma levels, and activity upon ICU admission, and patients who developed symptomatic TE (14%) had significantly higher MBL levels than patients without TE. MBL was strongly correlated to plasma D-dimer levels, a marker of COVID-19 coagulopathy, but showed no relationship to degree of inflammation or other organ dysfunction. In conclusion, we have identified complement activation through the MBL pathway as a novel amplification mechanism that contributes to pathological thrombosis in critically ill COVID-19 patients. Pharmacological targeting of the MBL pathway could be a novel treatment option for thrombosis in COVID-19. Laboratory testing of MBL levels could be of value for identifying COVID-19 patients at risk for TE events.

Fig. 1

Elevated mannose-binding lectin (MBL) levels and activity in critically ill COVID-19 patients are associated with thromboembolic events. ( A ) COVID-19 patients have elevated plasma MBL levels compared with healthy controls (625 kU/L [303–1,112] in the patient group [ n  = 65] vs. 444 kU/L [288–611] in controls [healthy blood donors, n  = 72], p  = 0.018). MBL was measured by an in-house sandwich enzyme-linked immunosorbent assay (ELISA) using a mouse monoclonal anti-MBL antibody (clone 3E7, Hycult Biotech) as capture antibody. The same antibody was biotinylated and used for detection together with streptavidin-horseradish peroxidase (HRP). ( B ) Elevated MBL pathway activity in COVID-19 patients measured as MBL binding activity (153% [53–223]), and MBL-dependent C3 deposition (157% [42–296]). MBL pathway activity was measured by a functional ELISA using mannan as MBL ligand. Microtiter plates were coated with 5 µg/mL mannan overnight and then incubated with plasma samples diluted in veronal-buffered saline at 37°C for 30 minutes. After washing, bound MBL and deposited C3 were detected by antibodies from R&D Systems (AF2307) and Complement Technology (A213), respectively, and HRP-conjugated secondary antibodies. Results are expressed as percentage of the activity of pooled normal human serum (NHS). The MBL activity assay showed a very good correlation with the MBL antigen assay (Spearman's r  = 0.94, p  < 0.0001). ( C – E ) COVID-19 patients who develop thromboembolic complications have elevated plasma MBL levels and activity. Of the nine patients who developed thrombosis seven had pulmonary embolism (indicated by black dots) and two arterial thromboses (indicated by circles). ( C ) MBL plasma levels (1,233 kU/L [721–1,623] in the thrombosis group vs. 470 kU/L [256–1,037] in patients with no thrombosis, p  = 0.0054); ( D ) MBL activity (221% [164–275] in the thrombosis group vs. 126% [45–215] in patients with no thrombosis, p  = 0.011); ( E ) C3 deposition (216% [144–496] in the thrombosis group vs. 129% [10–243] in patients with no thrombosis, p  = 0.028). Results are expressed as medians and interquartile ranges (IQRs). p -Values were calculated using the Mann–Whitney U test.