Platelet Sequestration in Man. II. Immunological and Clinical Studies*

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Abstract
The sequestration of Cr51-labeled human platelets after reaction in vivo with various amounts of isoantibody is studied. After combination with relatively small amounts of isoantibody, platelets were slowly destroyed in the spleen, whereas, with larger quantities, they were quickly destroyed in the liver. These patterns of sequestra-tion could be induced by concentrations of antibody undetectable by in vitro serologic techniques. The destruction of platelets by platelet isoantibodies was accompanied by leukopenia and typical pyrogenic reactions. In one case of chronic idiopathic thrombocytopenic purpura (FTP), transfused platelets were slowly destroyed in the spleen. Adrenocorticosteroids appeared to increase the circulating platelet level both by increasing platelet production and prolonging platelet survival. In a second patient, platelet survival was normal, and no organ accumulation of Cr51-labeled platelets occurred. In acute, severe ITP transfused platelets were rapidly destroyed in the liver. It appears to be generally true that platelets mildly damaged by immunologic or other means are destroyed in the spleen but severely damaged cells are removed from the circulation by the liver. The use of Cr51-labeled "citrate platelets" followed by body surface scanning may permit more accurate characterization of the thrombocytopenic disorders and aid in the selection of patients for splenectomy.