Masaaki Higashihara

Mastoparan, a wasp venom, activates platelets via pertussis toxin-sensitive GTP-binding proteins.

Mastoparan induced limited release of serotonin from intact human platelets, while neither intracellular calcium ion elevation nor arachidonic acid mobilization was observed. Cytolysis induced by mastoparan was negligible in the concentration range that induced serotonin release. In digitonin-permeabilized cells, mastoparan induced Ca(++)-independent release of serotonin and Ca(++)-dependent arachidonic acid release. Both serotonin release and arachidonic acid release were reduced by pertussis toxin, suggesting that platelet activation induced by mastoparan is mediated by GTP-binding proteins.

Increased secretion of lnterleukin-6 in malignant mesothelioma cells from a patient with marked thrombocytosis

Background. A high prevalence of thrombocytosis in malignant mesothelioma has been reported, although its pathogenesis remains unknown.

The platelet activation induced by wheat germ agglutinin

In human platelets, wheat germ agglutinin (WGA) induced serotonin release without cell agglutination. WGA induced the phosphorylation of both 40‐kDa and 20‐kDa proteins in a parallel manner, and at least, the phosphorylation of 40‐kDa protein was preceded by transient formation of endogenous diacylglycerol (DG) accompanied by a decrease in phosphatidylinositol (PI). Both phosphorylation of these two proteins and serotonin release were inhibited by prior treatment of platelets with dibutyryl cyclic AMP, W‐7, or TMB‐8. These results suggest that both phosphatidylinositol turnover and Ca2+ mobilization play an essential role in WGA‐induced platelet activation.

Thrombotic microangiopathy associated with alpha-interferon therapy for chronic myelocytic leukemia

A 31-year-old man diagnosed as having chronic myelocytic leukemia (CML) developed renal insufficiency with nephrotic-range proteinuria during alpha-interferon (IFN) therapy for CML. A renal biopsy specimen showed remarkable thrombotic microangiopathic lesions resembling those of hemolytic-uremic syndrome. The patient had papules on both lower legs, and a cutaneous biopsy showed similar microangiopathic lesions in dermal and subcutaneous vessels. Although discontinuation of IFN and initiation of prednisolone therapy resulted in resolution of proteinuria, renal insufficiency persisted. These findings suggest that long-term IFN therapy can induce late-onset thrombotic microangiopathy in systemic microvessels.

The role of apoE in inhibitory effects of apoE-rich HDL on platelet function

Apolipoprotein E‐ (ApoE‐) rich high‐density lipoprotein (HDL), which was prepared from the bound fraction of normolipemic volunteers on heparin‐Sepharose and from a hyperalphalipoproteinemic patient, potently inhibited aggregation of human platelets in a dose‐dependent fashion. Dimyristoyl phosphatidylcholine liposome with apoE (apoE · DMPC) also inhibited platelet aggregation, and incubation of washed platelets with apoE · DMPC resulted in the release of cholesterol into the supernatant in a time and dose‐dependent manner. These results suggest that apoE plays a major role in the inhibitory effect of apoE‐rich HDL in platelet function, presumably due to the release of cholesterol from the plasma membrane.

The novel variants of mb-1 and B29 transcripts generated by alternative mRNA splicing.

The Ig-alpha/Ig-beta heterodimers encoded by mb-1 and B29 genes, respectively, are crucial for the constitution of the B-cell receptor (BCR). We report here novel variants of mb-1 and B29 transcripts produced by alternative mRNA splicing. The proteins encoded by these variants are predicted to conserve transmembrane and cytoplasmic portions of Ig-alpha and Ig-beta but lack a part of the extracellular portions containing cysteine residues which are required for intramolecular and intermolecular S-S bonds. Transfection studies revealed that the variant mb-1 and B29 did not contribute to the BCR expression on cell surfaces. Although peripheral B cells contain small amounts of the variant mb-1 and B29 transcripts, treatment with an anti-IgM antibody, LPS or IL-4 induces a significant increase in amounts of the variant transcripts. These observations suggest that B-cell activation induces alternative splicing of mb-1 and B29 transcripts which encode proteins unable to constitute the BCR.

The inhibitory effects of okadaic acid on platelet function

Okadaic acid (OA), a potent inhibitor of protein phosphatases type 1 and type 2A, inhibited thrombin‐induced platelet aggregation (IC50 = 0.8 μM), [14C]serotonin release and increase in intracellular Ca2+ ([Ca2+]i) in the same dose dependence. In the absence of thrombin OA increased the phosphorylation of 50‐kDa protein and 20‐kDa myosin light chain (MLC20). The 50‐kDa protein phosphorylation was accomplished within a shorter time period and at a lower concentration than was the MLC20, OA decreased the thrombin‐induced phosphorylation of 47‐kDa protein and MLC20, although phosphorylation of MLC20 reincreased at higher concentrations of OA (5−10 μM). Since type 2A phosphatase is more sensitive to OA than type 1, these results suggest that type 2A phosphatases are involved in the regulation of Ca2+ signaling in thrombin‐induced platelet activation.

The platelet protein phosphorylation induced by a monoclonal antibody against human platelets (TP82)

In human platelets, a monoclonal anti-human platelet antibody (TP82) induced platelet aggregation and release of granules (i.e., serotonin, platelet factor 4, N-acetyl-beta-D-glucosaminidase). The release reaction occurred even in the absence of aggregation and was preceded by not only the protein phosphorylation, but the transient formation of endogenous diacylglycerol (DG). These results suggest that polyphosphoinositide breakdown plays an essential role in antibody-induced release of platelet granules.

Increased levels of soluble CD8 and CD4 in patients with infectious mononucleosis.

Plasma levels of soluble CD8 (sCD8) and soluble CD4 (sCD4) in 44 patients with infectious mononucleosis (IM) were studied. A marked increase in sCD8 (22366 +/- 2702 U/ml; control: 219 +/- 10 U/ml; P < 0.0001) and significant increase in sCD4 (19.3 +/- 0.9; control: 8.1 +/- 0.2, P < 0.0001) strongly suggest activation of both CD8+ and CD4+ lymphocytes, which is important in restraining Epstein-Barr virus-infected B lymphocytes. Levels of sCD8 strongly correlated with the percentage and the absolute number of both CD8+ and CD8(+)-HLA-DR+ lymphocytes. In addition, we showed increased release of sCD8 from lymphocytes in vitro and increased ratio between plasma sCD8 and the number of CD8+ lymphocytes in blood, indicating that elevation of plasma sCD8 is due to expansion of CD8+ subset as well as increased sCD8 release from each CD8+ cell. Increased sCD4 release from CD4+ lymphocytes, the number of which is not increased in the blood during IM, was also seen. Patients with more severe fever had higher levels of sCD8 and sCD4. During convalescence sCD8 and sCD4 levels showed progressive decrease; however, even at 60-119 d after onset the levels of sCD8 and sCD4 remained higher than normal, suggesting prolonged lymphocyte activation. These results suggest that sCD8 and sCD4 are useful in monitoring immune activation during IM.

A first case of complete remission of β-interferon sensitive adult T-cell leukemia

A case of complete remission of adult T‐cell leukemia (ATL) induced by β‐interferon is reported. A 46‐year‐old male was diagnosed as ATL because of the increased number of ATL cells with deeply indented and lobulated nuclei in the peripheral blood, accompanied by elevated values of the lactic dehydrogenase, the alkaline phosphatase, and the calcium in the serum. The result of the cell surface marker analysis of peripheral blood lymphocytes was compatible with ATL and anti‐ATL associated antibody (ATLA) was positive. The integration of proviral deoxyribonucleic acid (DNA) of human T‐cell leukemia virus type I(HTLV‐I) was proved in the peripheral blood lymphocytes using Southern blot hybridization. Since an ordinal chemotherapy was not so effective for this patient, he was treated with 1.8 times 107 units of recombinant β‐interferon (β‐IFN) per day for 7 days as one course. After 5 courses of treatment, a markedly favorable response was recognized, and he achieved complete remission. A lower dose of β‐IFN (9 times 106 units per day for 3 days as one course, one or two courses per month) has been continued and he has still been in a complete remission state for 10 months. It is concluded that β‐IFN should be used to treat ATL.