OC 05.4 - Biphasic thrombus formation and resolution during a coronavirus infection in the liver

Background: The liver is the main producer of coagulation factors, which are activated in response to a variety of viruses, presumably to contain and limit virus spreading. Neutrophils and their extracellular traps (NETs) often build the molecular and structural basis for such thrombi that can cause adverse complications and organ damage in patients. Using the murine coronavirus m-CoV, we analysed the consequences of a coronavirus infection in the liver.

Aims: Analysis of haemostatic alterations and immunothrombosis in a virus infected liver.

Methods: C57Bl/6 mice were nasally infected with m-CoV (MHV-A59). Livers were collected 2, 4 and 10 days after infection, and virus burden, tissue damage, thrombus formation, expression of coagulation factors and neutrophil activation were analysed via histology and qPCR.

Results: NET formation occurred rapidly and U-shaped over the course of the infection: 1.55 thrombi/mm2 liver section were present 2 days after m-CoV infection, which decreased to 0.50 thrombi/mm2 at day 4 and increased again to 1.04 thrombi/mm2 at day 10. Neutrophil counts significantly increased until day 4 and showed highest MPO activity on day 2. M-CoV virus is mainly present 4 days after infection and coincided with highest percentage of damaged tissue (4.58%). Although mRNAs of factors II, V, VII, VIII, IX, and X were not significantly altered, we could detect a significant peak in plasminogen mRNA on day 2 and PAI 1 mRNA on day 4. Plasma concentrations of MCP-1, IFN-γ, IL-6 and TNF α were also highest at day 4.

Conclusion(s): We describe a U-shaped liver thrombosis development during a coronavirus infection. Liver NETs are rapidly formed after a viral infection and are resolved due to increased plasminogen expression. Peak virus burden of the liver and increased systemic inflammation markers induce expression of liver PAI-1 and activation of recruited neutrophils, which favours NET formation anew.