Platelet migration inhibtion as an indicator of immunologically mediated target cell injury in canine ehrlichiosis.

A platelet migration inhibition test was devised to determine the presence of antiplatelet activity in serum collected from experimentally produced and natural cases of canine ehrlichiosis. The maximum platelet migration inhibition effect was observed during the acute phase of the disease and before the appearance of specific humoral antibody, measured by the indirect fluorescent-antibody test. Platelet migration inhibition may be one of the earliest events leading to pancytopenia. In most cases, sera positive for humoral antibodies also were positive for platelet migration inhibition, although no direct correlation was evident between the serological titer and the degree of platelet migration inhibition. Inoculation of dogs with uninfected canine blood did not induce the production of inhibition factor or antibody activity, which precluded a histocompatibility response to the cellular elements in the inoculum. Scanning electron microscopy indicated that the platelet inhibition factor interfered with platelet migration by inhibiting pseudopod formation. Affected platelets became rounded and showed evidence of clumping and leakage.