Drug-dependent and non-drug-dependent antiplatelet antibody in drug-induced immunologic thrombocytopenic purpura.

The mechanism of drug-dependent immunologic thrombocytopenic purpura (DITP) was investigated by studying the sera of four patients with classic DITP (two with quinidine-, one with acetaminophen-, and one with phenazopyridine-dependent antiplatelet antibody) using a solid-phase radioimmunoassay with 125I-staphylococcal protein A. Two forms of antiplatelet antibody could be demonstrated: one that required drug to bind to platelets and one that bound to platelets in the absence of drug. Drug-dependent antiplatelet antibody required the simultaneous addition of drug and the Fc domain of the drug-dependent IgG molecule for binding to platelets. It did not require serum complement or factor VIII-related antigen for binding to platelets. Drug-dependent binding of antibody to platelets was saturation-dependent. Non-drug-dependent antiplatelet antibody of two patients (one with quinidine-induced thrombocytopenia and the other with acetaminophen-induced thrombocytopenia) reacted with autologous platelets as well as with homologous platelets, indicating that they were autoantibodies. Both autoantibodies had disappeared when their sera were tested 23 and 138 days, respectively, after withdrawal of their initial positive sera. Non-drug-dependent antiplatelet antibody binding could be demonstrated with the F(ab')2 fragment of the purified IgG of the serum of the second patient with quinidine DITP, who did not have detectable alloantibodies against HLA. None of the four patients with non-drug-dependent antiplatelet antibody had a past or present history of autoimmune thrombocytopenic purpura.

Cumulative experience with a simplified solid-phase radioimmunoassay for the detection of bound antiplatelet IgG, serum auto-, allo-, and drug-dependent antibodies.

A simplified, sensitive, solid-phase radioimmunoassay employing 125I-staphylococcal protein A has been developed that is capable of detecting bound antiplatelet IgG as well as serum auto-, allo-, and drug-dependent antiplatelet antibodies. The simplified assay employs a ratio of test over control platelet counts per minute (cpm) for detection of positive results. All reagents are commercially available. The assay can be performed with as little as 10(6) washed platelets (10 microliters of whole blood) that have been stored for as long as 8 wk at 4 degrees C in microtiter plates. The assay time, employing stored platelets, is 4 hr. Bound platelet IgG is positive in 93% of 46 thrombocytopenic patients with autoimmune disease and correlates inversely with their platelet count, r = -0.65, p less than 0.001. The ability of this assay to detect serum antibody was studied with a rabbit anti-human platelet antibody capable of giving optimal immunoprecipitation with solubilized platelet membranes at a tier of 1:10. The present assay increases the sensitivity of antibody detection 256-fold to a titer of 1:2560. Human serum antiplatelet membrane antibody was positive in 2 of 2 patients with anti-PLA-1 antibody (titers of 1:256 and greater than 1:64); 7 of 12 multiply transfused patients who were refractory to platelet transfusion (2 had titers of greater than 1:256 and greater than 1:32); 5 of 19 patients with autoimmune thrombocytopenic purpura (2 had titers of 1:64 and 1:32); and 10 of 14 patients with clinical histories of drug-dependent antiplatelet antibody (2 had titers of 1:1280 for quinidine and 1:384 for phenazopyridine).

Cyclic adenosine 3':5'-monophosphate phosphodiesterase activity in normal and chronic lymphocytic leukemia lymphocytes.

The specific activity of cyclic adenosine 3':5'-monophosphate phosphodiesterase was measured in lymphocytes isolated from the blood of normal subjects, from patients with chronic lymphocytic leukemia, and from tonsil tissue. The mean specific activity of cyclic adenosine 3':5'-monophosphate phosphodiesterase in the lymphocytes from patients with untreated chronic lymphocytic leukemia was lower than that in lymphocytes from the blood of normal subjects or from tonsils. Cyclic adenosine 3':5'-monophosphate phosphodiesterase levels did not correlate with differences in B- and T-cell lymphocyte subpopulations or with peripheral blood lymphocyte counts.