Feline Leukemia Virus-Induced Thrombocytopenia and Macrothrombocytosis in Cats

The Kawakami-Theilen strain of feline leukemia virus (FeLV-KT), an exogenous anemia-inducing retrovirus, induced significant macrothrombocytosis and thrombocytopenia during acute infections of cats. The geometric mean platelet volumes of both freshly isolated fixed platelets and ethylenediamine tetraacetic acid-sphered platelets from infected cats were increased, but the ratio of fresh-fixed to ethylenediamine tetraacetic acid-sphered platelet volumes, an estimate of ethylenediamine tetraacetic acid-induced isovolumetric shape change, was normal. Total plasma membrane increased as the platelet volumes increased in FeLV-KT-infected cats, but estimated surface connected canalicular system surface area did not. Platelet concentrations were decreased 2 to 6 weeks after inoculation, but marked macrothrombocytosis resulted in a trend toward increased platelet mass on weeks 5 and 6 after inoculation. Thus, FeLV-KT-induced macrothrombocytosis may serve as a model of impaired platelet volume regulation. The platelet volume and platelet membrane surface area abnormalities found suggest that this model would allow studies of the megakaryocyte/platelet axis, particularly in the area of membrane formation and territorial demarcation.