The ability of mononuclear cells to coagulate blood in response to Coxiella burnetii.

Endocarditis is a rather frequent complication of Q fever caused by Coxiella burnetii. We examined the ability of phase I (virulent) or phase II (avirulent) C. burnetii to coagulate blood in the presence of human blood mononuclear cells in vitro. After incubation for 4 h, virulent phase I C. burnetii was an effective stimulant for mononuclear cells. Since this interaction is a potent trigger of blood coagulation through the extrinsic pathway, it could be responsible for the local deposition of fibrin on the surface of infected valves and the development of large vegetations in cases of endocarditis complicating Q fever.