In vitro infection by rickettsia conorii is associated to prothrombotic alterations of endothelial cells

S152

ABSTRACTS OF 12TH INTNAT’L CONGRESS

Vol. 65, SuppI. 1

P298

IL-4 INHlBITS

LPS-, ILlp-

OR TNFa-INDUCED

SUE FACTOR AND THROMBOMODULIN DOTHELIAL CELLS AND MONOCYTES, A. Dumas and J.M. Herbert, Sanofi Recherche,

EXPRESStON

OF TIS-

DOWN-REGULATION IN ENJ? Savi, M.CI Laplace, A. Lal4, F. Dot, Toulouse France.

Tissue factor (TF) is an ubiquitous membrane-anchored glycoprotein that initiates blood coagulation by forming a complex with circulating factors VII and Vlla. Under normal circumstances, endothelial ceils do not express TF activity while they constitutively express thrombomodulin ( TM ) which accelerates thrombin-catalysed activation of protein C thus contributing to the anticoagulant properties of the endothelium. In some pathological situations, when the endothelium or the monocytes are exposed to inflammatory mediators, they can acquire procoagulant pro-perties. Endotoxin (LPS), IL1 6 and TNFa increased the expression of TF on the surface of cultured bovine aortic (ABAE) or human umbilical vein endothelial cells (HUVEC) and human monocytes while they simultaneously reduced the amount of TM on the endothelial cell surface. On endothelial cells and monocytes, interleukin4 (IL-4) strongly inhibited LPS-induced TF expression but a similar activity was also obtained with regard to the effects of IL1 or TNF. Simultaneously, IL-4 counteracted TM down-regulation consecutive to an incubation of endothelial cells with LPS, IL1 or TNF. These results therefore show that IL-4 protects the endothelial cell and the monocyte surface against inflammatory mediators-induced procoagulant changes. P299 IN VITRO INFECTION BY RICKETTSIA CONORII IS ASSOCIATEDTO PROTHROMBOTIC ALTERATIONS OF ENDOTHELIAL CELLS D. Arnoux, N. Teysseirel, E George, B. Bout&e, D. Raoultl and J. Sampol Lab. Hematologie, Hop. Conception’ Unite des Rickettsies CHU Timone, Marseille, F In Mediterranean Spotted Fever, the vascular endothelium represents the target cell of the infectious agent, Rickettsia conorii (RC). This rickettsiosis is often associated in vivo to thromboembolic complications. In order to investigate the prothmmbotic mechanisms involved in this pathology, we have evaluated the following parameters on human umbilical endothelial cells infected in vitro by RC: functional and ant$enic expression of thrombomoduhn (TM) and Tissue Factor (TF) and release of van Willebraad factor (VWF). Sequential assays were camed out between 2 and 24 hours post-infection. Cell-associated TM activity was determined by a chromogenic method using purified human thrombin and protein C. Tissue factor activity was measured in the cell extracts by a one stage clotting assay,using either normal pooled plasma or FVlll deficient plasma. TM, TF and VWF cellular aotigenic expression was quantified by flow cytometry. VWF was evaluated in the culture supematants by an Elisa assay.When compared to non infected controls, TM activity and antigen regularly decreased between 4 and 24 hours post infection. TF activity became detectable at 2 H, reached a maximum at 4 H and progressively decreased thereafter. TF antigen followed a similar kinetics. Infection resulted in a rapid decrease of cellular VWF, associated to a delayed accumulation in the culture supematants. These early disturbances of vascular endothelium may provide a support for the thrombotic aspect of Mediterranean Spotted Fever.