Factor Xa and Factor VIIa Utilize Herpes Simplex Virus-Associated Tissue Factor to Increase Infection through Cellular Protease Activated Receptor 2.

Abstract 2130

Poster Board II-107

We have shown previously that purified herpes simplex type-1 (HSV1) can initiate coagulation on its surface because of tissue factor (TF) derived from the host cell and virus-encoded glycoprotein C (gC). Generation of thrombin by this viral surface pathway correlated to an increase in the susceptibility of cells to infection through a mechanism involving protease activated receptor (PAR) 1. Incomplete inhibition of the serum-mediated increase in infection by hirudin indicated that mechanisms in addition to thrombin are involved. To further investigate the importance of coagulation enzymes in HSV1 infection, the current study investigated the upstream activated coagulation factors X (FXa) and VII (FVIIa). Using a novel panel of viruses deficient in either TF and/or gC in cytolytic viral plaque assays, we examined the contribution of viral TF and gC in the FXa- or FVIIa- mediated infection of human umbilical vein endothelial cells. The addition of purified FXa resulted in up to 400% enhancement of infection when TF and gC were on the virus surface. Similarly, the effect of FVIIa was maximal when TF and gC were present, although only 150% increased. In agreement with previous studies, the addition of purified thrombin resulted in approximately a 500% increase in infection using the novel panel of viruses, which unlike FXa and FVIIa was not dependent on either viral TF or gC. Simultaneous addition of FXa/FVIIa or thrombin/FXa/FVIIa further enhanced infection to a maximum of 10-fold. FX alone had no effect on infection; however, in situ FXa generation due to the addition of FVIIa increased infection. The involvement of PAR2 was shown using inhibitory PAR2 specific antibodies which attenuated the effects of FXa and FVIIa. Anti-PAR1 inhibited the effect of thrombin, but had no effect on either FXa- or FVIIa-dependent infection. The importance of viral TF was demonstrated by inhibition of FXa or FVIIa-mediated plaque formation by anti-TF antibody, which had an insignificant effect on TF-deficient HSV1. Collectively, these data indicate that FXa and FVIIa together with TF on the virus surface may activate cellular PAR2 to increase HSV1 infection independent of thrombin.