Li and He [.] found PAR-4 protein expression but failed to detect the presence of PAR-4 transcripts due to technical issues. Irrespectively, also in our hands, PAR-4 expression is marginal. The presence of PAR-1, -3 and -4 at protein level in naïve monocytes suggests that cross-talking between coagulation and inflammation is possible, because PARs are sensitive to protease stimulation. Human PAR-1 can be activated by FXa and thrombin; whereas PAR-2 can be activated by FVIIa, the binary TF-FVIIa complex, FXa and the Crizotinib cell line ternary TF-FVIIa-FXa complex; and PAR-3 and PAR-4 can be activated by thrombin [5-7, 13]. PAR activation is irreversible. Upon activation, PARs are uncoupled from signalling and then
internalized CAL-101 chemical structure and degraded [26, 27]. Therefore, we first investigated whether stimulation of naïve monocytes with the coagulation proteases would alter PAR expression. The percentage monocytes expressing PARs and the MFI of PAR expression did not
changed upon stimulation, with the coagulation proteases suggesting that PARs were not activated and internalized . We next investigated whether stimulation of naïve monocytes with coagulation proteases resulted in cytokine production. It is known that coagulating whole blood results in the production of IL-6 and IL-8 . In addition, administration of FVIIa was found to elicit IL-6 and IL-8 release in healthy human subjects . In our study, none of the investigated coagulation proteases induced pro-inflammatory cytokine production by naïve CD14+ monocytes. For FVIIa and the binary TF-FVIIa complex, this seems logic
regarding the absence of PAR-2 expression on naïve monocytes. For FXa and thrombin, our findings correspond to previous studies demonstrating that both FXa and thrombin did not promote monocyte IL-1β, IL-6 and TNF-α secretion [31-33]. Thus, although freshly isolated naïve monocytes express PAR-1, PAR-3 and PAR-4 at protein level, our results demonstrate that stimulation with the investigated coagulation Ixazomib supplier proteases does not result in cross-talking with the inflammation cascade leading to pro-inflammatory cytokine production. To figure out which coagulation protease is responsible for the observed pro-inflammatory cytokine release in coagulating whole blood and upon FVIIa administration in vivo, we next investigated whether stimulation of PBMCs with coagulation proteases resulted in pro-inflammatory cytokine release and proliferation. From the investigated coagulation proteases, only thrombin was found to induce pro-inflammatory effects. Thrombin-induced IL-1β and IL-6 cytokine release and PBMC cell proliferation. This effect clearly appeared to be PAR-1 mediated. Because isolated CD14+ monocytes did not respond, it could be that the context of PBMC population is necessary to stimulate the monocytes. On the other hand, it is also plausible that other cells within the PBMC population were stimulated by thrombin.