alpha-chymotrypsin and Thrombocytopenia

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.

Topics: Animals; Autoantibodies; Chymotrypsin; Epitopes; Humans; Immunoblotting; Immunoglobulin G; Immunosorbent Techniques; Mice; Peptide Fragments; Platelet Membrane Glycoproteins; Quinidine; Quinine; Thrombocytopenia

A new platelet alloantigen, Sra, is described that was defined by an alloantibody detected in the serum of a healthy mother who delivered a child with typical clinical signs of neonatal alloimmune thrombocytopenia (NAIT). The antibody reacted strongly with the child's and father's platelets, but not with platelets of the mother or with those of a highly selected panel representing all known platelet alloantigens. Platelets from 300 unselected normal blood donors also tested negative, suggesting a phenotype frequency in the German population of less than 0.01. The antigen was present in 9 of 20 members within three generations of the paternal family, indicating autosomal codominant inheritance. By immunochemical analysis using a glycoprotein (GP)-specific immunoassay and a variety of GP IIb/IIIa-specific monoclonal antibodies for antigen immobilization (MAIPA assay), radioimmunoassay, and Western blotting, we could show that the antigen resides on a 68-Kd proteolytic fragment of GP IIIa. Immunogenetic data and gene dosage studies revealed that the Sra antigen is not related to any of the other known platelet alloantigens. In accordance with established criteria, the Sra antigen represents the first example of a "private" platelet alloantigen that bears significance in rare instances of NAIT.

Topics: Adult; Antibodies, Monoclonal; Blood Platelets; Blotting, Western; Chymotrypsin; Female; Gene Frequency; Humans; Immunoassay; Immunosorbent Techniques; Infant, Newborn; Isoantigens; Peptide Fragments; Phenotype; Platelet Membrane Glycoproteins; Radioimmunoassay; Thrombocytopenia; Trypsin

The effect of experimental trypanosomiasis on coagulation was studied because a patient in this hospital with Rhodesian trypanosomiasis developed thrombocytopenia with disseminated intravascular coagulation. Rats injected intraperitoneally with this strain of Trypanosoma rhodesiense consistently developed trypanosomiasis and severe thrombocytopenia without changes in hematocrit or concentration of fibrinogen or fibrin split products. At the time of 50% mortality (4-5 days) mean platelet counts per cubic millimeter of infected rats were 18,000+/-9,000 (+/-2 SEM) compared to 1,091,000+/-128,000 in uninfected controls. In vitro, concentrated trypanosomes and trypanosomefree supernates of disrupted organisms added to normal rat, rabbit, or human blood produced platelet aggregation within 30 min. This platelet aggregation was not blocked by inhibitors of ADP, kinins, or early or late components of complement. In vivo thrombocytopenia also occurred in infected rabbits congenitally deficient in C6 and in infected, splenectomized rats. Although the aggregating substance obtained from disrupted trypanosomes is heat-labile, it is active in the presence of complement inhibitors, suggesting that this trypanosomal product may be a protein enzyme or toxin. Since the phenomenon is independent of immune complexes, complement, ADP, and kinins, it appears to represent a new mechanism of microbial injury of platelets and the induction of thrombocytopenia.

Topics: Adenosine; Adenosine Diphosphate; Animals; Blood Cell Count; Blood Platelets; Chymotrypsin; Complement System Proteins; Disseminated Intravascular Coagulation; Edetic Acid; Fibrin; Fibrinogen; Hematocrit; Humans; In Vitro Techniques; Male; Microscopy, Electron; Platelet Adhesiveness; Rabbits; Rats; Thrombocytopenia; Trypanosomiasis; Trypsin; Trypsin Inhibitors