The use of allele-specific PCR for platelet alloantigen typing should facilitate the development of DNA-based typing in other regional blood centers and clinical laboratories.

We studied ten normal subjects and 20 patients with stable, untreated idiopathic thrombocytopenic purpura (ITP) and platelet counts in the range of 35,000 to 110,000/microL. The diagnosis was made by clinical criteria. Platelet-associated IgG was increased in all nine of the nine patients studied. Autologous platelets were labeled with chromium 51 and reinfused for measurement of mean cell life and platelet production rate. Mean cell life was calculated by two methods, weighted mean and multiple hit, with excellent agreement between the two. As expected, mean cell life was significantly reduced in ITP patients as compared to the normal subjects (2.9 days v. 8.0 days, P less than .001). However, mean platelet production rates in ITP patients and normal subjects, 3.5 and 3.8 X 10(9) platelets/k/d respectively, were not significantly different. Platelet production rate was above and below the normal range (2 to 5.6 X 10(9) platelets/k/d) in two and four patients, respectively. We conclude that the rate of platelet production is not increased in most patients with ITP who have platelet counts greater than 35,000/microL. We did find that platelet size was increased in eight of the 12 patients in whom it was measured, including two of the patients with low platelet production.

Serial studies were performed in two patients with cyclic thrombocytopenia to investigate the pathogenesis of this disorder. Mean life span of autologous platelets when platelet levels were declining was subnormal (2.4 and 0.8 days), and megakaryocytes were abundant in the bone marrow during thrombocytopenia. Megakaryocyte colony- stimulating activity could not be detected in the serum of either patient at any point of their cycles. In each patient, total platelet- associated IgG varied inversely with platelet levels. Surface platelet- associated IgG was measured only in patient 2 and was significantly elevated (greater than 1,280 IgG molecules per platelet) at all stages of the cycle, even during thrombocytosis. However, the highest values were observed during thrombocytopenia. Platelet-bindable IgG in plasma declined to normal immediately before platelet levels began to rise. IgG eluted from the platelets of this patient reacted strongly with autologous and homologous platelets in contrast to a “mock eluate” prepared from platelets of a normal subject. The eluate from the patient's platelets reacted strongly with immobilized autologous and homologous glycoprotein IIb/IIIa complex and weakly with GPIb but not with isolated GPIIIa alone. In each patient the decline in platelet levels was significantly delayed following administration of intravenous gamma globulin 0.4 g/kg body weight for five days. These findings suggest that platelet-reactive autoantibodies are of pathogenic significance in some patients with cyclic thrombocytopenia.

With data on 91 alloimmunized thrombocytopenic patients and 389 donor- recipient pairs matched or selectively mismatched for HLA antigens, it was observed that ABO incompatibility significantly reduced the effectiveness of platelet transfusions. The mean 24-hr recovery of platelets from histocompatible donors and from donors selectively mismatched for cross-reactive HLA antigens was decreased by approximately 23% if the donor typed for blood group A and/or B not found in the recipient. Thus, the reduction in platelet recovery associated with ABO incompatibility is not of a magnitude that would contraindicate transfusion of ABO-mismatched platelets.

Recent studies have shown that antibodies characteristic of quinine- and quinidine-induced thrombocytopenia sometimes recognize the platelet membrane glycoprotein (GP) complex IIb/IIIa in addition to their well known target, GPIb/IX. We have investigated the frequency with which drug-induced antibodies bind to GPIIb/IIIa and the nature of their target epitopes. In studies of sera from 13 patients sensitive to quinidine or quinine, we found that 10 contained IgG antibodies specific for both GPIb/IX and GPIIb/IIIa, two reacted with GPIb/IX alone, and one reacted with GPIIb/IIIa alone. In all cases, the presence of drug was required for binding of IgG to target GPs. By immunoabsorption, we found that each of five polyspecific sera contained at least two different antibodies, one reactive with GPb/IX and the other with GPIIb/IIIa. Further studies with eight drug- dependent antibodies (DDAb) specific for GPIIb/IIIa showed that three recognized the GPIIb/IIIa complex only, one recognized GPIIb alone, and three recognized GPIIIa alone. The eighth serum appeared to bind to both GPIIIa alone and to an epitope determined by the GPIIb/IIIa complex. The three antibodies specific for GPIIIa alone also reacted with GPIIIa deglycosylated with endo-H, and with the major (61 Kd) fragment obtained by chymotryptic digestion of GPIIIa but failed to react with reduced GPIIIa. These findings demonstrate that, in drug- induced, immunologic thrombocytopenia, the anti-platelet immune response is typically directed against epitopes on both GPIb/IX and GPIIb/IIIa. The three DDAb we studied that were specific for GPIIIa alone recognize epitopes resistant to chymotrypsin and endo-H treatment that are dependent on intrachain disulfide bonding.