Plasma exchange is the commonly considered therapy for the treatment of thrombotic microangiopathy (TMA); however, it is not always mandatory. We treated a patient who presented with malignant hypertension (MH) complicated by TMA using antihypertensive therapy that was not accompanied by plasma exchange. A 38-year-old woman with photophobia, diarrhea, fever, and severely elevated blood pressure was referred to our hospital. Blood test results revealed thrombocytopenia and hemolytic anemia, and ascites were observed on the computed tomography images. Although TMA was suspected, plasma exchange was not performed because the platelet count was not markedly low. Her blood cell counts improved after antihypertensive treatment, and she was discharged. The patient is currently under therapy and remains stable. Thus, TMA secondary to MH may improve using antihypertensive therapy, without the need for invasive plasma exchange. Considering the platelet count may be helpful in deciding whether plasma exchange is required.
The platelet binding properties of human monoclonal lupus autoantibodies have been studied. These IgM autoantibodies, produced by human X human hybridomas derived from lymphocytes of patients with systemic lupus erythematosus, are known to bind to single-stranded DNA. Four anti-DNA antibodies that express the dominant 16/6 idiotype--HF2′1/17, HF2′18/2, HF2′1/13b, and HF3′16/6--bound to glutaraldehyde-fixed platelets. In contrast, HF6′21/28, HF9′11/3, and polyclonal IgM bound poorly to platelets. [35S]Methionine was incorporated into HF2′1/17, and the interaction of the intrinsically radiolabeled HF2′1/17 with fixed platelets was evaluated in a solution phase radioimmunoassay. [35S]Methionine HF2′1/17 bound to fixed platelets and could be displaced by equivalent amounts of HF2′1/17, HF2′18/2, HF2′1/13b, and HF3′16/6. HF2′1/17 bound with greater affinity to fresh platelets and to thrombin-activated platelets than to glutaraldehyde-fixed platelets. Single-stranded DNA competed with platelets for the HF2′1/17 combining site. Treatment of fresh platelets with nuclease I, trypsin, chymotrypsin, and neuraminidase did not alter the binding of antibody to the platelet surface. No binding of antibody to phospholipid micelles was observed. Purified IgM autoantibodies did not inhibit platelet aggregation induced with ADP, thrombin, or ristocetin in platelet-rich plasma. These results indicate that the human IgM monoclonal anti-DNA autoantibodies that express the dominant 16/6 idiotype are polyspecific, bind to platelets, and interact with a platelet epitope that does not appear to involve DNA, protein, or sialic acid. These antibodies interact with platelets through the same sites responsible for antibody-DNA binding.
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