Cyclic thrombocytopenia of apparent autoimmune etiology

Abstract

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.

Maternal alloimmunization against the rare platelet‐specific antigen HPA‐9b (Maxa) is an important cause of neonatal alloimmune thrombocytopenia

“…Soluble immune complexes consisting of antibody bound to GPIIb/IIIa are then captured with a GPIIb/IIIa-specific MoAb and the associated human antibody is detected with appropriate secondary reagents. 22 The inconsistent and relatively weak reactions of the maternal serum samples with GPIIb/IIIa from HPA-9b (Max a )-positive paternal PLTs in solid-phase assays and with recombinant GPIIb/IIIa bearing the HPA-9b mutation is in distinct contrast to antibodies reactive with HPA-1a (Pl A1 ), which routinely give strong positive reactions in these assays. Failure of the antibodies to react with paternal GPIIb/IIIa in the ACE assay was not due to competition between anti-HPA-9b (Max a ) and AP2, the MoAb used to immobilize the target GPIIb/IIIa complex because AP2 was suitable for detection of anti-HPA-9b in the MACE assay and can be used to detect most HPA-3b (Bak b )specific antibodies, 28 which recognize an epitope at position 843 in the GPIIb heavy chain only six residues away from the HPA-9b (Max a ) site at position 837.…”

“…6,20 Antibodies recognizing glycoprotein complexes GPIIb/IIIa, Ib/IX, Ia/IIa, GPIV, and Class I HLA were detected in solid-phase enzyme-linked immunosorbent assays (ELISAs) with antigen capture ELISA (ACE) 21 and modified antigen capture ELISA (MACE). 22 The normal PLT panel used in these assays contained at least one member carrying each of the…”

Severe neonatal alloimmune thrombocytopenia caused by antibodies to human platelet antigen 3a (Baka) detectable only in whole platelet assays

“…12 The antibody in Mother B was identified from its reaction pattern against a panel of PLTs in flow cytometry. 13 The two antibodies were further characterized with flow cytometry, antigen capture ELISA (ACE), 14 modified antigen capture ELISA (MACE), 15 and MoAb Immobilization of PLT antigens (MAIPA) 16 assay. In ACE, PLTs are solubilized in Triton X-100 detergent and GPIIb and GPIIIa present in the lysate is captured in microtiter plate wells containing immobilized MoAb AP2 specific for the GPIIb-GPIIIa complex.…”

Isoimmunization against CD36 (glycoprotein IV): description of four cases of neonatal isoimmune thrombocytopenia and brief review of the literature

“…Details of the assay have been described previously. 13 Characterization of mutations in the CD36 gene CD36 mutations were identified by direct sequencing of the CD36 promoter and exons following amplification of genomic DNA by PCR. PCR components were purified with columns (Centricon 100, Millipore, Watford, UK) or with a kit (QIAquick Gel Extraction kit, Qiagen, Crawley, UK) when necessary.…”