Evaluation of the ability of commercial enzyme-linked immunosorbent assays to measure mouse tissue factor

Background: Tissue factor (TF) is the primary cellular initiator of the blood coagulation cascade. Increased levels of TF expression on circulating monocytes or on extracellular vesicles (EVs) are associated with thrombosis in a variety of diseases, including sepsis and COVID-19. Objectives: Here, we aimed to evaluate the ability of 4 commercial TF enzyme -linked immunosorbent assays (ELISAs) to measure mouse TF in cells and plasma. Methods: We used 4 commercial mouse TF ELISAs (SimpleStep, R&D Systems, MyBioSource [sandwich], and MyBioSource [competitive]). We used recombinant mouse TF (rmTF; 16-1000 pg/mL), cell lysates from a TF-expressing mouse pancreatic cancer cell line, and plasma and EVs isolated from plasma from mice injected with vehicle or bacterial lipopolysaccharide (LPS). Results: The 2 MyBioSource kits failed to detect rmTF or TF in cell lysates. The SimpleStep and R&D kits detected rmTF in buffer or spiked into plasma in a concentrationdependent manner. These kits also detected TF in cell lysates from a mouse pancreatic cancer cell line. A higher signal was observed with the SimpleStep kit compared to the R&D kit. However, the SimpleStep and R&D kits failed to detect TF in plasma or EVs from LPS-treated mice. Conclusion: Our results indicate that some commercial ELISAs can be used to measure mouse TF levels in cell lysates but they cannot detect TF in plasma or EVs from endotoxemic mice.