Toxic granulation neutrophils and C-reactive protein.
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C-Reactive Protein↗
Biomedical subjects
Y Kanakura
Publications and source records attributed to Y Kanakura.
Biologic significance of GATA-1 activities in Ras-mediated megakaryocytic differentiation of hematopoietic cell lines.
Lineage-specific transcription factors play crucial roles in the development of hematopoietic cells. In a previous study, it was demonstrated that Ras activation was involved in thrombopoietin-induced megakaryocytic differentiation. In this study, constitutive Ras activation by H-ras(G12V) evoked megakaryocytic maturation of erythroleukemia cell lines F-36P and K562, but not of myeloid cell line 32D cl3 that lacks GATA-1. However, the introduction of GATA-1 led to reprogramming of 32D cl3 toward erythrocytic/megakaryocytic lineage and enabled it to undergo megakaryocytic differentiation in response to H-ras(G12V). In contrast, the overexpression of PU.1 and c-Myb changed the phenotype of K562 from erythroid to myeloid/monocytic lineage and rendered K562 to differentiate into granulocytes and macrophages in response to H-ras(G12V), respectively. In GATA-1-transfected 32D cl3, the endogenous expression of PU.1 and c-Myb was easily detectable, but their activities were reduced severely. Endogenous GATA-1 activities were markedly suppressed in PU.1-transfected and c-myb-transfected K562. As for the mechanisms of these reciprocal inhibitions, GATA-1 and PU.1 were found to associate through their DNA-binding domains and to inhibit the respective DNA-binding activities of each other. In addition, c-Myb bound to GATA-1 and inhibited its DNA-binding activities. Mutant GATA-1 and PU.1 that retained their own transcriptional activities but could not inhibit the reciprocal partner were less effective in changing the lineage phenotype of 32D cl3 and K562. These results suggested that GATA-1 activities may be crucial for Ras-mediated megakaryocytic differentiation and that its activities may be regulated by the direct interaction with other lineage-specific transcription factors such as PU.1 and c-Myb.
Animals↗
Full oncogenic activities of v-Src are mediated by multiple signaling pathways. Ras as an essential mediator for cell survival.
Tyrosine kinase oncoproteins cause simultaneous activation of multiple intracellular signaling pathways. However, the precise mechanisms by which individual pathways induce oncogenesis are not well understood. We have investigated the roles of individual signaling pathways in v-Src-dependent cell growth and survival by inhibiting one particular pathway. v-Src induced constitutive activation of signal transducers and activators of transcription 3 (STAT3), phosphatidylinositol 3-kinase, and Ras in murine Ba/F3 cells and led to factor-independent proliferation. Dominant-negative mutants of STAT3 (STAT3D) and phosphatidylinositol 3-kinase (Deltap85) inhibited v-Src-dependent growth by approximately 60 and approximately 40%, respectively. Moreover, dominant-negative Ras (N17) induced severe apoptosis, which was accompanied by down-regulation of Bcl-2 and activation of caspase-3. Although cells overexpressing Bcl-2 or caspase-3 inhibitors remained viable even when N17 was expressed, the growth was reduced by approximately 85%. During N17- and STAT3D-induced growth suppression, expression of cyclin D2, cyclin D3, c-myc, and c-fos was suppressed by N17, whereas that of cyclin D2, cyclin E, and c-myc was suppressed by STAT3D. Thus, v-Src-activated Ras and STAT3 are involved in distinct but partly overlapping transcriptional regulation of cell cycle regulatory molecules. These results suggest that the full oncogenic activity of v-Src requires simultaneous activation of multiple signalings, in which Ras is particularly required for survival.
Animals↗
Specific c-kit mutations in sinonasal natural killer/T-cell lymphoma in China and Japan.
Sinonasal lymphoma is one of the constituents of lethal midline granuloma, which is a clinical term for progressive, destructive lesions affecting the midline of the face. The majority of sinonasal lymphomas, especially those showing polymorphous patterns of proliferation and thus termed polymorphic reticulosis, recently were categorized as sinonasal natural killer/T-cell lymphomas. They are more prevalent in Asia than Europe or North America and are associated with EBV infection. Twenty-three cases with sinonasal natural killer/T-cell lymphomas were collected from two high-incidence regions: Beijing, China (14 cases) and Osaka, Japan (9 cases). c-kit mutations were analyzed on paraffin-embedded specimens by PCR-single-strand conformation polymorphism followed by direct sequencing; the c-kit proto-oncogene encodes a receptor of tyrosine kinase, which plays an important role in the regulation of normal and neoplastic hematopoiesis by the interaction with its specific ligand, termed stem cell factor. Twelve single nucleotide substitution mutations were seen in 23 cases. Ten of 14 Chinese cases (71.4%) had mutations at exon 11 or exon 17, whereas only two of nine Japanese cases (22.2%) had mutations, showing a significant difference in frequency between Chinese and Japanese cases. Furthermore, seven of eight mutations (92%) in exon 17 occurred at codon 825 and three of four mutations (75%) in exon 11 occurred at codon 561. Such a specificity has not been reported before, and these results, taken together, suggest that location-specific differences in etiological factors cause specific mutations in c-kit gene.
Adolescent↗
Induction of apoptosis by extracellular ubiquitin in human hematopoietic cells: possible involvement of STAT3 degradation by proteasome pathway in interleukin 6-dependent hematopoietic cells.
The ubiquitin-proteasome pathway is responsible for selective degradation of short-lived cellular proteins and is critical for the regulation of many cellular processes. We previously showed that ubiquitin (Ub) secreted from hairy cell leukemia cells had inhibitory effects on clonogenic growth of normal hematopoietic progenitor cells. In this study, we examined the effects of exogenous Ub on the growth and survival of a series of human hematopoietic cells, including myeloid cell lines (HL-60 and U937), a B-cell line (Daudi), and T-cell lines (KT-3, MT-4, YTC-3, and MOLT-4). Exogenous Ub inhibited the growth of various hematopoietic cell lines tested, especially of KT-3 and HL-60 cells. The growth-suppressive effects of Ub on KT-3 and HL-60 cells were almost completely abrogated by the proteasome inhibitor PSI or MG132, suggesting the involvement of the proteasome pathway in this process. Furthermore, exogenous Ub evoked severe apoptosis of KT-3 and HL-60 cells through the activation of caspase-3. In interleukin-6 (IL-6)-dependent KT-3 cells, STAT3 was found to be conjugated by exogenous biotinylated Ub and to be degraded in a proteasome-dependent manner, whereas expression levels of STAT1, STAT5, or mitogen-activated protein kinase were not affected. Moreover, IL-6-induced the up-regulation of Bcl-2 and c-myc, and JunB was impaired in Ub-treated KT-3 cells, suggesting that the anti-apoptotic and mitogenic effects of IL-6 were disrupted by Ub. These results suggest that extracellular Ub was incorporated into hematopoietic cells and mediated their growth suppression and apoptosis through proteasome-dependent degradation of selective cellular proteins such as STAT3. (Blood. 2000;95:2577-2585)
Apoptosis↗
Increased D-type cyclin expression together with decreased cdc2 activity confers megakaryocytic differentiation of a human thrombopoietin-dependent hematopoietic cell line.
At the late phase of megakaryocytopoiesis, megakaryocytes undergo endomitosis, which is characterized by DNA replication without cell division. Although a number of cell cycle regulatory molecules have been identified, the precise roles of these molecules in megakaryocytic endomitosis are largely unknown. In a human interleukin-3-dependent cell line transfected with the thrombopoietin (TPO) receptor c-mpl (F-36P-mpl), either treatment with TPO or the overexpression of activated ras (Ha-Ras(G12V)) induced megakaryocytic maturation with polyploid formation. We found that TPO stimulation or Ha-Ras(G12V) expression led to up-regulation of cyclin D1, cyclin D2, and cyclin D3 expression. In addition, expression levels of cyclin A and cyclin B were reduced during the total course of both TPO- and Ha-Ras(G12V)-induced megakaryocytic differentiation, thereby leading to decreased cdc2 kinase activity. Neither the induced expression of cyclin D1, cyclin D2, or cyclin D3 nor the expression of a dominant negative form of cdc2 alone could induce megakaryocytic differentiation of F-36P-mpl cells. In contrast, overexpression of dominant negative cdc2 together with cyclin D1, cyclin D2, or cyclin D3 facilitated megakaryocytic differentiation in the absence of TPO. These results suggest that both D-type cyclin expression and decreased cdc2 kinase activity may participate in megakaryocytic differentiation.
CDC2 Protein Kinase↗
GATA-1 blocks IL-6-induced macrophage differentiation and apoptosis through the sustained expression of cyclin D1 and bcl-2 in a murine myeloid cell line M1.
Cytokines exert pleiotropic effects on target cells in a manner dependent on the cell type or stage of differentiation. To determine how instinctive cell properties affect biological effects of cytokine, we introduced an erythroid/megakaryocyte lineage-specific transcription factor, GATA-1, into a murine myeloid cell line M1, which is known to undergo macrophage differentiation in response to interleukin 6 (IL-6). Overexpression of GATA-1 changed the phenotype of M1 cells from myeloid to megakaryocytic lineage. Furthermore, GATA-1 blocked both IL-6-induced macrophage differentiation and apoptosis of M1 cells. Although STAT3 is essential for IL-6-induced macrophage differentiation of M1 cells, GATA-1 had little or no effect on tyrosine phosphorylation, DNA binding, and transcriptional activities of STAT3 in Western blot analysis, electropholic mobility shift assay (EMSA), and luciferase assays. During IL-6-induced macrophage differentiation of M1 cells, IL-6 down-regulated cyclin D1 expression and induced p19(INK4D) expression, leading to reduction in cdk4 activities. In contrast, sustained expression of cyclin D1 and a significantly lesser amount of p19(INK4D) induction were observed in IL-6-treated M1 cells overexpressing GATA-1. Furthermore, although bcl-2 expression was severely reduced by IL-6 in M1 cells, it was sustained in GATA-1-introduced M1 cells during the culture with IL-6. Both IL-6-induced macrophage differentiation and apoptosis were significantly abrogated by coexpression of cyclin D1 and bcl-2, whereas overexpressions of cyclin D1 or bcl-2 inhibited only differentiation or apoptosis, respectively. These results suggested that GATA-1 may not only reprogram the lineage phenotype of M1 cells but also disrupt the biologic effects of IL-6 through the sustained expression of cyclin D1 and bcl-2. (Blood. 2000;95:1264-1273)
Animals↗
Epstein-Barr virus associated B-cell lymphoma of brain developing in myelodysplastic syndrome with c-kit mutation (Try-557 -->stop).
The first case of B-cell lymphoma of brain in a patient with myelodysplastic syndrome (MDS) was reported. A 68-year-old man was admitted because of anemia, fever, and thrombocytopenia and was diagnosed as having MDS (refractory anemia with excess of blasts) on the basis of the findings of bone marrow aspiration and chromosomal analysis. The patient was followed up without chemotherapy, but a brain tumor appeared after 3 years. Histologic and immunohistologic examinations revealed diffuse large B-cell lymphoma. Mutations of the c-kit proto-oncogene (stem cell factor receptor) and the p53 tumor-suppressor gene were examined in the MDS lesion and malignant lymphoma (ML) by the polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP) method followed by direct sequencing. The p53 mutation was not found in either MDS or ML, but a nonsense mutation (Try-557 --> stop) in exon 11 of the c-kit, which might lead to dysfunction of tyrosine kinase activity, was detected in MDS. This is the first report of c-kit mutation in MDS. Epstein-Barr virus (EBV) genome was demonstrated in the nucleus of brain ML cells by in situ hybridization with EBV-encoded RNA-1 probe. Immunohistochemistry showed that the tumor cells expressed latent infection gene products, including EBV nuclear antigen-2 and latent membrane protein-1. This pattern of latent gene expression was Lat III, which is usually found in malignant lymphomas developing in immunocompromised hosts. These findings suggest that a profound pancytopenia in MDS resulted in an immunodeficient condition, after which EBV-positive B-cell lymphoma of brain developed.
Aged↗
Detection of small populations of CD59-deficient erythrocytes in patients with aplastic anemia or myelodysplastic syndrome and normal individuals.
To detect a small population of blood cells with a deficiency of glycosyl phosphatidylinositol (GPI)-anchored protein, we evaluated the expression of CD59 by flow cytometry on one million erythrocytes, which is about 100 times more than the number of erythrocytes tested by our standard immunoassay. Blood samples from healthy volunteers, patients with aplastic anemia (AA), and patients with myelodysplastic syndrome (MDS), who all showed no detectable GPI deficiency by the standard assay, were investigated. The numbers of CD59-deficient erythrocytes were 5 to 145/10(6) erythrocytes in the healthy volunteers (mean 29.2), and one of the volunteers had an increase in the deficient cells exceeding the mean + 3 SD (141.7), a normal limit. A CD59-deficient population was detected in 6 of the 21 (28.6%) patients with AA and 5 of the 18 (27.8%) patients with MDS. The new assay was performed again in 5 of these 11 patients and the normal individual who had the CD59-deficient populations at 6 and 12 months after the initial study. The number of deficient cells gradually increased in 1 patient with MDS (from 511 to 2892/10(6) erythrocytes), while the numbers of the other 4 patients showed a tendency to decline, although the deficient populations were repeatedly detected on most of the occasions. Changes in the number of the deficient cells were also seen in the healthy volunteer, but they were rather rapid; the numbers changed from 145 to 5661 and then to 18/10(6) erythrocytes within 3 months. The CD59 assay used in this study is easy to perform and enabled us to detect less than 1% GPI-deficient cells.
Adolescent↗
Blastic transformation of splenic lymphoma with villous lymphocytes after a well-controlled chronic phase of more than 10 years.
A 30-year-old Japanese man with splenomegaly and lymphocytosis was examined in 1985. Blood analysis revealed that some of the lymphocytes had short-surface villi with polar distribution. The cells showed Ig lambda+, CD5+, CD11c+, CD19+, CD22+, CD23+, CD24+, FMC7+ phenotype. A small M peak was detected in the serum. Splenic lymphoma with villous lymphocytes (SLVL) was diagnosed on the basis of these findings. Remission was induced and was maintained with low-dose chlorambucil for more than 10 years. In 1996, the patient developed splenomegaly and lymphadenopathy with "B" symptoms and a high serum lactase dehydrogenase (LDH) level. Large blastoid cells with prominent nucleoli were observed in the bone marrow; later, a small number appeared in the peripheral blood. The bone marrow cells showed a complex chromosomal abnormality involving del(7)(q32). Southern blot analysis of immunoglobulin gene rearrangements in SLVL cells that had been cryopreserved in 1986 and of bone marrow cells in 1996 showed 2 rearranged bands in each cell sample; 1 band showed identical sizes in the 2 samples, and the other showed different sizes. These findings suggest that the blastoid cells were derived from SLVL cells through transformation. After this transformation, the disease followed a highly aggressive course. Various chemotherapeutic agents had little effect, and the patient died 3 months later.
Adult↗
[TPO/c-mpl and hematopoietic stem cells].
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Animals↗
Stromal cell CD9 regulates differentiation of hematopoietic stem/progenitor cells.
CD9 belongs to the transmembrane 4 superfamily, and has been shown to influence cell proliferation, motility, and adhesion. We show here that ligation of CD9 modifies proliferation and/or differentiation of hematopoietic stem/progenitors. Pluripotent EML-C1 hematopoietic cells were cocultured with MS-5 stromal cells in the presence of KMC8.8, an anti-CD9 antibody. Numbers of recovered EML-C1 cells were slightly reduced and the antibody caused the hematopoietic cells to migrate beneath the adherent stromal cell layer. Of particular interest, EML-C1 cells recovered from CD9-ligated cultures had undifferentiated properties. Separate pretreatment of the two cell types with antibody showed that stromal-cell CD9 mediated these responses. Spontaneous expression of erythroid marker was completely blocked and there was a shift towards undifferentiated clonogenic progenitors. Immunoprecipitation studies showed that stromal-cell CD9 associates with the beta1 subunit of integrin, as well as a novel 100 kD protein. Antibody cross-linking of cell surface CD9 increased the amount of 100 kD protein that was subsequently coprecipitated with CD9. These observations show that stromal-cell CD9 influences physical interactions with hematopoietic cells and may be one factor that determines the degree of stem cell differentiation.
Animals↗
Transcriptional regulation of the cyclin D1 promoter by STAT5: its involvement in cytokine-dependent growth of hematopoietic cells.
STAT5 is a member of a family of transcription factors that participate in the signal transduction pathways of many hormones and cytokines. Although STAT5 is suggested to play a crucial role in the biological effects of cytokines, its downstream target(s) associated with cell growth control is largely unknown. In a human interleukin-3 (IL-3)-dependent cell line F-36P-mpl, the induced expression of dominant-negative (dn)-STAT5 and of dn-ras led to inhibition of IL-3-dependent cell growth, accompanying the reduced expression of cyclin D1 mRNA. Also, both constitutively active forms of STAT5A (1*6-STAT5A) and ras (H-rasG12V) enabled F-36P-mpl cells to proliferate without added growth factors. In NIH 3T3 cells, 1*6-STAT5A and H-rasG12V individually and cooperatively transactivated the cyclin D1 promoter in luciferase assays. Both dn-STAT5 and dn-ras suppressed IL-3-induced cyclin D1 promoter activities in F-36P-mpl cells. Using a series of mutant cyclin D1 promoters, 1*6-STAT5A was found to transactivate the cyclin D1 promoter through the potential STAT-binding sequence at -481 bp. In electrophoretic mobility shift assays, STAT5 bound to the element in response to IL-3. Furthermore, the inhibitory effect of dn-STAT5 on IL-3-dependent growth was restored by expression of cyclin D1. Thus STAT5, in addition to ras signaling, appears to mediate transcriptional regulation of cyclin D1, thereby contributing to cytokine-dependent growth of hematopoietic cells.
Cell Cycle↗
Activating mutation in the catalytic domain of c-kit elicits hematopoietic transformation by receptor self-association not at the ligand-induced dimerization site.
The c-kit receptor tyrosine kinase (KIT) is constitutively activated by naturally occurring mutations in either the juxtamembrane domain or the kinase domain. Although the juxtamembrane domain mutations led to ligand-independent KIT dimerization, the kinase domain mutations (Asp814 --> Val or Tyr) did not. In an effort to determine if the kinase domain mutant could transfer oncogenic signaling without receptor dimerization, we have constructed the truncated types of c-kitWild and c-kitTyr814 cDNAs (c-kitDel-Wild and c-kitDel-Tyr814 cDNAs, respectively), in which ligand-binding and ligand-induced dimerization domains were deleted. When c-kitDel-Wild and c-kitDel-Tyr814 genes were introduced into a murine interleukin-3 (IL-3)-dependent cell line Ba/F3, KITDel-Tyr814 was constitutively phosphorylated on tyrosine and activated, whereas KITDel-Wild was not. In addition, Ba/F3 cells expressing KITDel-Tyr814 (Ba/F3(Del-Tyr814)) grew in suspension culture without the addition of exogenous growth factor, whereas Ba/F3 cells expressing KITDel-Wild (Ba/F3(Del-Wild)) required IL-3 for growth. The factor-independent growth of Ba/F3(Del-Tyr814) cells was virtually abrogated by coexpression of KITW42 that is a dominant-negative form of KIT, but not by that of KITWild, suggesting that KITDel-Tyr814 may not function as a monomer but may require receptor dimerization for inducing factor-independent growth. Furthermore, KITDel-Tyr814 was found to be coimmunoprecipitated with KITWild or KITW42 by an ACK2 monoclonal antibody directed against the extracellular domain of KIT. Moreover, KITW42 was constitutively associated with a chimeric FMS/KITTyr814 receptor containing the ligand-binding and receptor dimerization domain of c-fms receptor (FMS) fused to the transmembrane and cytoplasmic domain of KITTyr814, but not with a chimeric FMS/KITWild receptor even after stimulation with FMS-ligand. These results suggest that constitutively activating mutation of c-kit at the Asp814 codon may cause a conformation change that leads to receptor self-association not in the extracellular domain and that the receptor self-association of the Asp814 mutant may be important for activation of downstream effectors that are required for factor-independent growth and tumorigenicity.
Animals↗
Both Stat3-activation and Stat3-independent BCL2 downregulation are important for interleukin-6-induced apoptosis of 1A9-M cells.
A unique subclone of a bone marrow-derived stromal cell line, BMS2.4, produces soluble factors that inhibit proliferation of several types of hematopoietic cell lines. An understanding of these molecules may be informative about negative regulatory circuits that can potentially limit blood cell formation. We used expression cloning to identify interleukin-6 (IL-6) as one factor that suppressed growth of a pre-B-cell variant line, 1A9-M. Moreover, IL-6 induced macrophage-differentiation and apoptosis of 1A9-M cells. During this process, IL-6 downregulated expression of BCL2 in 1A9-M cells and stimulated BCL-XL expression, but had no effect on p53, Bax, or Bak gene expression. Mechanisms for transduction of IL-6-induced signals were then evaluated in IL-6-stimulated 1A9-M cells. Whereas the signal transducer and activator of transcription 3 (Stat3) was phosphorylated and activated, there was no effect on either Stat1 or Stat5. The importance of BCL2 and Stat3 on IL-6-induced macrophage-differentiation and apoptosis was studied with 1A9-M cells expressing human BCL2 or a dominant-negative form of Stat3, respectively. IL-6-induced apoptosis, but not macrophage-differentiation, was blocked by continuously expressed BCL2. A dominant-negative form of Stat3 inhibited both macrophage-differentiation and apoptosis induced by IL-6. However, diminished Stat3 activity did not prevent IL-6-induced downregulation of the BCL2 gene. Therefore, activation of Stat3 is essential for IL-6-induced macrophage-differentiation and programmed cell death in this model. Whereas overexpression of BCL2 abrogates the apoptotic response, Stat3-independent signals appear to downregulate expression of the BCL2 gene.
Apoptosis↗
Uterine reconstruction for complete septate uterus.
In the period between 1990-1995, six women with complete septate uterus presented to our clinic and underwent uterine reconstruction using our own unique procedure, a method we independently developed using the Jones & Jones procedure and the Thompkins procedure for reference. Five of these 6 cases later became pregnant, and to date, they have given birth to 7 newborns. Because of a very high rate of successful postoperative pregnancy, we were convinced that uterine reconstruction is useful for complete septate uterus.
Cesarean Section↗
Functional roles of thrombopoietin-c-mpl system in essential thrombocythemia.
Thrombopoietin (TPO) is implicated as a primary regulator of megakaryopoiesis and thrombopoiesis through binding to the cytokine receptor c-Mpl (the product of the c-mpl-proto-oncogene). In addition to its physiologic role, the TPO-c-mpl system has been suggested to participate in the pathophysiology of essential thrombocythemia (ET) which is a clonal disorder characterized by a sustained elevation of the circulating platelet count and bone-marrow hyperplasia with excessive proliferation of megakaryocytes. Recent studies have demonstrated that serum TPO levels are slightly elevated or within normal range in ET patients, whereas serum TPO levels tend to be inversely correlated with platelet mass. Flow cytometric, Western blot, and Northern blot analyses have revealed that the expression of platelet c-Mpl is strikingly reduced in all of patients with ET, possibly due to the decreased expression of c-mpl mRNA. These results suggest that normal or slightly elevated levels of serum TPO in ET patients may be attributable to the impaired uptake and catabolism of TPO owing to the low c-Mpl expression. Furthermore, immunoblotting with anti-phosphotyrosine antibody showed that no aberrant protein-tyrosine phosphorylation was observed in platelets of ET patients before treatment with TPO, and the levels of TPO-induced protein-tyrosine phosphorylation, including c-Mpl-tyrosyl phosphorylation, roughly paralleled those of c-Mpl expression, suggesting that c-Mpl-mediated signaling pathway was not constitutively activated in platelets of ET patients. Although activating mutation in the TPO gene, which leads to overexpression of TPO mRNA, has been reported in familial thrombocythemia, these results suggest that TPO-c-Mpl system may not be directly linked to pathogenesis of sporadic ET.
Humans↗
Platelet activation induced by combined effects of anticardiolipin and lupus anticoagulant IgG antibodies in patients with systemic lupus erythematosus--possible association with thrombotic and thrombocytopenic complications.
Antiphospholipid antibodies (aPL) are well known to be associated with arterial and venous thrombosis. In a series of 180 patients with systemic lupus erythematosus (SLE), the prevalence of arterial thrombosis was obviously higher in the patients who had both anticardiolipin antibodies (aCL) and lupus anticoagulant (LA) (17/35, 48.6%, p<0.05) (Table 1) than in the other patients bearing aCL or LA alone or neither of them (2/145, 1.4%). Since a substantial fraction of the former group of patients with arterial thrombosis also had thrombocytopenia (12/17, 70.6%), there was a possibility that aCL and LA might have enhanced platelet activation and aggregation. To test this possibility, we studied the in vitro effects of aCL and LA on the enhancement of platelet activation by flow cytometric analysis using anti-CD62P and anti-CD41 monoclonal antibodies directed against platelet activation-dependent granule-external membrane (PADGEM) protein and platelet glycoprotein IIb (GPIIb), respectively. Platelet activation defined by the surface expression of CD62P was not induced by aCL+ x LA+ plasma only, but was significantly augmented by aCL+ x LA+ plasma in combination with adenosine diphosphate (ADP) at a low concentration that had only a modest effect on platelet activation. In contrast, aCL+ x LA-, aCL- x LA+ and aCL- x LA- plasma samples were incapable of enhancing platelet activation in the presence or absence of ADP stimulation. In addition to plasma samples, the purified IgG from aCL+ x LA+ plasma (aCL+ x LA+-IgG) also yielded apparent enhancement of platelet activation induced by ADP. Furthermore, platelet activation was generated by the mixture of aCL+ x LA--IgG and aCL- x LA+-IgG fractions prepared from individual patients, but not by each fraction alone. These results suggest that aCL and LA may cooperate to promote platelet activation, and may be involved, at least partially, in the pathogenesis of arterial thrombosis and thrombocytopenia in patients with SLE.
Adolescent↗