Experimental immunologic thrombocytopenia in dogs: a study of thrombocytopenia and megakaryocytopoiesis.

Immunologic thrombocytopenia was induced in dogs by intravenous or intraperitoneal injection of rabbit anti-canine platelet serum (APS) or by intraperitoneal injection of the IgG fraction of the APS. In contrast, dogs injected with normal rabbit serum (NRS) or the IgM fraction of the APS did not develop thrombocytopenia. Marrow samples obtained at 24-96 h after inoculation of the IgG fraction contained megakaryocytes giving a positive reaction with flurescein isothiocyanate or horseradish peroxidase-conjugated anti-rabbit globulin. In contrast, negative results were obtained with megakaryocytes in marrow samples collected before injection of the IgG fraction or after injection of the IgM fraction or NRS. The attachment of anti-platelet antibody to the surface of megakaryocytes was associated with appearance of morphologic abnormalities, particularly in mature megakaryocytes. Simultaneously, the number of immature megakaryocytes and acetylcholine esterase (AChE)-positive small cells (presumably megakaryocyte precursors) increased considerably. These changes coincided with the development of thrombocytopenia, and subsided as recovery ensued.