FXIIa generation was measured with a chromogenic substrate. of plasma in a FIX-dependent manner. In a purified system, the activation of FXII and PK by long polyP promoted FIX activation and prothombin activation. In an model of occlusive thrombus formation, inhibition of FXIIa with CTI but not of FXI with a neutralizing antibodies abolished the prothrombotic effect of long polyP. Conclusions We propose that long polyP promotes FXII-mediated blood coagulation bypassing FXI. Accordingly, some polyP containing pathogens may have evolved strategies to exploit polyP-initiated FXII activation for virulence, and selective inhibition of FXII may improve the host response to pathogens. 0.05) As shown in figure 3C, addition of FXIIa to plasma in the presence of FXa inhibitors accelerated clotting from ~1000 sec to ~90 sec in a concentration-dependent manner. We observed that the pretreatment of plasma with 14E11 or 1A6 did not inhibit the procoagulant effect of -FXIIa. However, the ability of -FXIIa to promote the plasma clotting was abrogated by the presence of CTI (Fig. 3C). PolyP promotes FXII and PK activation and the activation of FXI by thrombin, but not by FXIIa We next designed experiments to determine whether polyP Rabbit polyclonal to NEDD4 promotes FXII activation in a purified system. We found that Spinosin long, but not short polyP increased the rate of Spinosin FXII activation in presence of PK and HK. (Fig. 4A), confirming the observation that long polyP of the size accumulated in bacteria are more potent at activating the contact pathway than polyP of the size present in platelets [5]. We found that long and short polyP did not increase FXII autoactivation (Fig. S4A). We next investigated whether long polyP could directly promote PK activation. As shown in figure 4B, long and short polyP enhanced the rate of PK autoactivation. Furthermore, our data show that activation of PK by FXIIa was significantly increased Spinosin by long, but not short polyP (fig. 4C). Open in a separate window Figure 4 PolyP promotes FXII and PK activation and the activation of FXI by thrombin, but not by FXIIa(A) FXII activation was measured in a purified system following the addition of 200 nM FXII, 50 nM PK and 50 nM HK in the presence of vehicle () or 5 M long () or short () polyP. FXIIa generation was measured with a chromogenic substrate. (B) PK autoactivation following addition of 200 nM PK and 200 nM HK in the presence of vehicle () or 5 M long () or short () polyP. Kallikrein generation was measured with a chromogenic substrate. (C) PK activation following addition of 50 nM PK, 50 nM HK and 100 pM FXIIa in the presence of vehicle () or 5 M long () or short () polyP. Kallikrein generation was measured with a chromogenic substrate. (D) FXI activation was measured following addition of 5 M long () or short () polyP to 30 nM FXI. In separate experiments, 5 nM -thrombin was added to 30 nM FXI in the presence of vehicle () or 5 M long () or short () polyP. FXIa generation was measured with a chromogenic substrate. (E) FXI activation following addition of 30 nM FXI and 5 nM -FXIIa in the presence of vehicle () or 5 M long () or short () polyP. FXIa generation was measured with a chromogenic substrate. (F) FXI activation following addition of 50 nM FXI, 200 nM FXII, 50 nM PK and 50 nM HK in the presence of vehicle () or 5 M long () or short () polyP. FXIa generation was measured with a chromogenic substrate. Data are mean SE (n = 3). We next designed experiments Spinosin to determine whether polyP promotes FXI activation in a purified system. As shown in figure 4D, long, but not short polyP enhanced the rate of FXI activation by -thrombin. We found that dextran sulfate increased.