In vitro effect of Leptospira icterohaemorrhagiae on human mononuclear leukocytes: comparison of virulent with non virulent strain.

The in vitro effect of a virulent and a non virulent strain of Leptospira interrogans serotype icterohaemorrhagiae on human peripheral mononuclear cells was investigated. After addition of bacteria to citrated whole blood the production of mononuclear cell procoagulant activity (tissue factor) was observed. Indeed mononuclear cells isolated from whole blood-bacteria mixtures after prolonged incubation shortened the recalcification time of normal plasma. The virulent strain induced a significantly higher procoagulant activity than non virulent and this effect was dependent on the number of bacteria. The production of tissue factor, a potent trigger of blood clotting, by Leptospira icterohaemorrhagiae could help to understand the mechanism(s) responsible for the activation of intravascular coagulation sometimes associated with leptospirosis.