The presence and specificity of antiplatelet autoantibodies in 32 patients with primary and 18 patients with secondary autoimmune thrombocytopenic purpura (AITP), as well as 11 non-thrombocytopenic patients with systemic autoimmune diseases, were studied. By means of the direct and indirect monoclonal antibody immobilization of platelet antigen (MAIPA) assay, antiplatelet autoantibodies were detected using monoclonal antibodies specific for platelet glycoproteins (GPs) Ib, IIb/IIIa, Ia/IIa, and IV. Serum antiplatelet autoantibodies were found in 18 of 32 primary AITP patients (56%), 6 of 18 secondary AITP patients (33%), and 5 of 11 nonthrombocytopenic patients (45%). Platelet-associated autoantibodies were detected in five of eight patients with primary (62%) and in four of eight patients with secondary AITP (50%) and in two of four patients without thrombocytopenia (50%). Multiple antibody reactivity, mainly against GPs IIb/IIIa and Ib and, in a few patients, against Ia/IIa, was found. Using MAIPA, platelet xylene eluates from 20 patients were also studied. Antiplatelet elutable autoantibodies were related to thrombocytopenia; autoantibodies against membrane GPs Ib and IIb/IIIa were demonstrable in 84 and 63% of eluates from patients with primary and secondary AITP, respectively, but not in eluates from nonthrombocytopenic patients. The presence of antiplatelet antibodies thus appears to be a common feature of many autoimmune diseases apart from the thrombocytopenia, but the (primary or secondary) etiology of the immune thrombocytopenia cannot be differentiated on the grounds of their specificity.

We studied 47 subjects belonging to 13 unrelated families with a history of mild haemorrhagic diathesis and chronic thrombocytopenia. 36 patients presented some degree of thrombocytopenia: 7/36 (19%) had slight thrombocytopenia (100–150×109/L); 26/36 (72%) had mild thrombocytopenia (50–100×109/L) and 3/36 (8%) had severe thrombocytopenia (<50×109/L). No correlation was observed between platelet count and the degree of haemorrhagic diathesis, which was mild in the majority of patients. Transmission was autosomal dominant. Platelet anisocytosis, increased percentage of large platelets and absence of leukocyte inclusions were observed in 26/30 (87%) of the examined blood smears. The ultrastructural appearance of platelets was normal. Megakaryocytes appeared normal in number in 10/10 patients, but showed asynchronous nuclear‐cytoplasm maturation and mainly nonlobulated nuclei. Platelet aggregation was studied in 26 patients and either increased or decreased curves were variably observed in response to different aggregating agents. Platelet‐associated IgG (PAIgG) was increased in 18/31 (58%) patients, while serum autoantibodies against platelet glycoproteins Ib/IX or IIb/IIIa were demonstrable in only 1 case. An increased expression of platelet surface glycoproteins Ib and IIb/IIIa, as studied by murine monoclonal antibodies binding in 17 cases, was observed. Platelet survival performed by 111In‐oxine‐labelled autologous platelets was normal in the 3 studied patients. Congenital macrothrombocytopenia confirms to be a distinct clinical disorder for which the name of “chronic isolated hereditary macrothrombocytopenia” is proposed.

We performed a retrospective study on the prevalence of heparin-induced thrombocytopenia (HIT) in 233 patients receiving hog mucosa heparin therapy. Of these, 82 patients received s.c. calcium heparin, 130 patient received unfractionated (UF) i.v. heparin, and 21 patients received low molecular weight heparins (LMWH). An additional four patients, referred to our consultation and diagnosed by us as having clinically active type II HIT (HIT-II) were also studied. The mean platelet count of the 233 patients receiving heparin showed a significant decrease after 2 days of heparin treatment and a following significant increase 6 days later (basal: 257 ± 147 x 10 9 platelets/L; day 2: 239 ± 122, p < 0.0002; day 6: 286 ± 119, p < 0.004). Of the 212 patients receiving UF heparin, 13 (6%) fulfilled the criteria for HIT-II: seven of these had received i.v. heparin (mean daily dose 26,600 ± 4,082 IU & p l u s m n ; SD) and six had received s.c. heparin (mean daily dose 21,428:t 6,900 IU). Their mean basal platelet count was 226 & p l u s m n ; 100 SD × 10 9 platelets/L and the nadir during heparin treatment was 78 ± 39 x 10 9 platelets/L. Thrombotic complications occurred in four (30.7%) of the 13 patients with HIT-II. Since the immunological mechanism has been demonstrated for HIT-II and since platelet factor 4 (PF4) was identified as the co-factor for the binding of heparin-related antibodies, we set up our own enzyme-linked immunosorbent assay (ELISA) for testing antibodies against PF4/heparin complex bound through electrostatic bridges to the solid phase. The highest binding capacity of HIT-related IgG to the multimolecular complex was obtained at 20 μg/ml for PF4 and 3 μg/ml for heparin, corresponding to 250 ng of PF4 and 42 ng of heparin in each microtiter well. Such binding was inhibited in a dose-dependent manner by increasing amounts of heparin, protamine hydrochloride, and a monoclonal antibody anti-human PF4 clone 1OB2. We observed that HIT-related antibodies bound also to PF4/LMWH complexes but the optimal PF4/glycosaminoglycan ratio appeared more critical for LMWH (enoxaparin, fraxiparin, and pamaparin) than for UF heparin. Sera from eight patients with HIT-II were tested by PF4/heparin ELISA; six of these had IgG against the complex PF4/heparin and three also had IgM. The persistence of HIT-related antibodies was investigated in three patients: in one such antibodies were still detectable 3 years after the acute episode, while in the other two, they disappeared after 6 months and 1 year, respectively.

Hepatitis C virus (HCV), an RNA virus, is known to be the major cause of post-transfusion non-A, non-B hepatitis. HCV can induce several expressions of autoimmunity, including both serological abnormalities and clinical disorders. The relationship between the HCV infection and anti-platelet autoimmunity has been occasionally described, but is still far from well-defined. We retrospectively analysed 101 serum specimens, collected between 1988 and 1994, from patients with immune thrombocytopenia (ITP) for the presence of anti-HCV antibodies. Eighty-seven patients were classified as having idiopathic, and 14 secondary ITP (4 systemic lupus erythematosus, 9 non-Hodgkin's lymphoma and 1 Evan's syndrome). Anti-HCV antibodies were determined by second generation tests (ELISA + RIBA). A specimen was considered positive for HCV antibodies in the presence of ELISA reactivity (sample optical density/cut-off > 1.00) accompanied by RIBA reactivity to at least one HCV specific antigen. 20 sera (20%) were positive, with a prevalence higher in secondary than in idiopathic ITP (43% vs. 16%, p < 0.05). No differences were found between anti-HCV positive and negative patients regarding gender, platelet count, platelet associated immunoglobulins, hepatitis B virus serology and liver enzyme profile. On the contrary, mean age was higher in the HCV positive vs HCV negative ones (58±18SD vs. 44±20yrs, p < 0.01), in keeping with the increasing prevalence of HCV infection with ageing. HCV positive patients, showed a poor response to treatment (platelet count lower than 50,000/μl after conventional medical therapy for immune thrombocytopenia) compared to anti-HCV negative ones, (50% versus 7.3%, p < 0.001). When we excluded patients who were exposed to risk factors for HCV infection after ITP diagnosis and before the serum collection, the prevalence of anti-HCV antibodies was not very different (17.6%) from that found in the series as a whole (19.8%). Our results seem to indicate that HCV infection may play a role in triggering several cases ITP, and moreover might constitute a negative prognostic factor for therapy response.