High-yield production of recombinant platelet factor 4 by harnessing and honing the gram-negative bacterial secretory apparatus.

Platelet factor 4 is a cytokine released into the bloodstream by activated platelets where it plays a pivotal role in etiology and diagnosis of heparin-induced thrombocytopenia. Therefore, a sustainable source of recombinant PF4 with structural and functional similarity to its native form is urgently needed to be used in diagnostic procedures. To this end, a three-in-one primary construct was designed from which three secondary constructs can be derived each capable of employing either type I, type II secretory or cytoplasmic pathways. Protein expression and secretion were performed in Escherichia coli BL21 (DE3) and confirmed by SDS-PAGE and Western blotting. To further enhance protein secretion, the effect of several controllable chemical factors including IPTG, Triton X-100, sucrose, and glycine were individually investigated at the outset. In the next step, according to a fractional factorial approach, the synergistic effects of IPTG, Triton X-100, and glycine on secretion were further investigated. To ascertain the structure and function of the secreted recombinant proteins, dynamic light scattering was utilized to confirm the rPF4 tetramerization and heparin-mediated ultra-large complex formation. Moreover, Raman spectroscopy and Western blotting were exploited to evaluate the secondary and quaternary structures, respectively. The type II secretory pathway was proven to be superior to type I in the case of rPF4 secretion. Supplementation with chemical enhancers improved the protein secretion mediated by the Type II system to approximately more than 500 µg/mL. Large quantities of native rPF4 up to 20 mg were purified as the culture medium was scaled up to 40 mL. Western blotting confirmed the formation of dimers and tetramers in the secreted rPF4 proteins. Dynamic light scattering revealed the rPF4 oligomerization into of larger complexes of approximately 100-1200 nm in size following heparin supplementation, implying proper protein folding and tetramerization. Moreover, the rPF4 secondary structure was found to be 43.5% Random coil, 32.5% ß-sheet, 18.6% α-helix and 4.9% Turn, which is in perfect agreement with the native structure. Our results indicate that the gram-negative type II bacterial secretory system holds a great promise as a reliable protein production strategy with industrial applications. However, further efforts are required to realize the full potential of secretory pathways regarding their application to proteins with distinct characteristics.

Dynamic intercellular redistribution of HIT antigen modulates heparin-induced thrombocytopenia.

Heparin-induced thrombocytopenia (HIT) is a prothrombotic disorder initiated by antibodies to platelet factor 4 (PF4)/heparin complexes. PF4 released from platelets binds to surface glycosaminoglycans on hematopoietic and vascular cells that are heterogenous in composition and differ in affinity for PF4. PF4 binds to monocytes with higher affinity than to platelets, and depletion of monocytes exacerbates thrombocytopenia in a murine HIT model. Here we show that the expression of PF4 on platelets and development of thrombocytopenia are modulated by the (re)distribution of PF4 among hematopoietic and endothelial cell surfaces. Binding of PF4 to platelets in whole blood in vitro varies inversely with the white cell count, likely because of the greater affinity of monocytes for PF4. In mice, monocyte depletion increased binding of PF4 to platelets by two- to three-fold. Induction of HIT in mice caused a transient >80-fold increase in binding of HIT antibody to monocytes vs 3.5-fold increase to platelets and rapid transient monocytopenia. Normalization of monocyte counts preceded the return in platelet counts. Exposure of blood to endothelial cells also depletes PF4 from platelet surfaces. These studies demonstrate a dynamic interchange of surface-bound PF4 among hematopoetic and vascular cells that may limit thrombocytopenia at the expense of promoting prothrombotic processes in HIT.

Platelets Drive Inflammation and Target Gray Matter and the Retina in Autoimmune-Mediated Encephalomyelitis.

Despite growing evidence for platelets as active players in infection and immunity, it remains unresolved whether platelets contribute to, or are key elements in the development of neuroinflammation. Using the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis, we identified platelet accumulation in the circulation by 7-day postinduction (dpi), ahead of clinical onset which occurs at 13-14 dpi. By inducing platelet depletion between 7 and 16 dpi, we demonstrate an association between platelet accumulation in the spinal cord and disease development. Additionally, we provide evidence for platelet infiltration in the white and gray matter parenchyma, but with different outcomes. Thus, while in white matter platelets are clearly associated with lesions, in gray matter large-scale platelet infiltration and expression of the platelet-specific molecule PF4 are detectable prior to T cell entry. In the retina, platelet accumulation also precedes clinical onset and is associated with significant increase in retinal thickness in experimental relative to control animals. Platelet accumulation increases over the disease course in this tissue, but without subsequent T cell infiltration. These findings provide definitive confirmation that platelet accumulation is key to EAE pathophysiology. Furthermore, they suggest an undescribed and, most importantly, therapeutically targetable mechanism of neuronal damage.

Overexpression of the transcription factor Sp1 activates the OAS-RNAse L-RIG-I pathway.

Deregulated expression of oncogenes or transcription factors such as specificity protein 1 (Sp1) is observed in many human cancers and plays a role in tumor maintenance. Paradoxically in untransformed cells, Sp1 overexpression induces late apoptosis but the early intrinsic response is poorly characterized. In the present work, we studied increased Sp1 level consequences in untransformed cells and showed that it turns on an early innate immune transcriptome. Sp1 overexpression does not activate known cellular stress pathways such as DNA damage response or endoplasmic reticulum stress, but induces the activation of the OAS-RNase L pathway and the generation of small self-RNAs, leading to the upregulation of genes of the antiviral RIG-I pathway at the transcriptional and translational levels. Finally, Sp1-induced intrinsic innate immune response leads to the production of the chemokine CXCL4 and to the recruitment of inflammatory cells in vitro and in vivo. Altogether our results showed that increased Sp1 level in untransformed cells constitutes a novel danger signal sensed by the OAS-RNase L axis leading to the activation of the RIG-I pathway. These results suggested that the OAS-RNase L-RIG-I pathway may be activated in sterile condition in absence of pathogen.

Specific molecular signatures predict decitabine response in chronic myelomonocytic leukemia.

Myelodysplastic syndromes and chronic myelomonocytic leukemia (CMML) are characterized by mutations in genes encoding epigenetic modifiers and aberrant DNA methylation. DNA methyltransferase inhibitors (DMTis) are used to treat these disorders, but response is highly variable, with few means to predict which patients will benefit. Here, we examined baseline differences in mutations, DNA methylation, and gene expression in 40 CMML patients who were responsive or resistant to decitabine (DAC) in order to develop a molecular means of predicting response at diagnosis. While somatic mutations did not differentiate responders from nonresponders, we identified 167 differentially methylated regions (DMRs) of DNA at baseline that distinguished responders from nonresponders using next-generation sequencing. These DMRs were primarily localized to nonpromoter regions and overlapped with distal regulatory enhancers. Using the methylation profiles, we developed an epigenetic classifier that accurately predicted DAC response at the time of diagnosis. Transcriptional analysis revealed differences in gene expression at diagnosis between responders and nonresponders. In responders, the upregulated genes included those that are associated with the cell cycle, potentially contributing to effective DAC incorporation. Treatment with CXCL4 and CXCL7, which were overexpressed in nonresponders, blocked DAC effects in isolated normal CD34+ and primary CMML cells, suggesting that their upregulation contributes to primary DAC resistance.

In vitro hematological and in vivo vasoactivity assessment of dextran functionalized graphene.

The intravenous, intramuscular or intraperitoneal administration of water solubilized graphene nanoparticles for biomedical applications will result in their interaction with the hematological components and vasculature. Herein, we have investigated the effects of dextran functionalized graphene nanoplatelets (GNP-Dex) on histamine release, platelet activation, immune activation, blood cell hemolysis in vitro, and vasoactivity in vivo. The results indicate that GNP-Dex formulations prevented histamine release from activated RBL-2H3 rat mast cells, and at concentrations ≥ 7 mg/ml, showed a 12-20% increase in levels of complement proteins. Cytokine (TNF-Alpha and IL-10) levels remained within normal range. GNP-Dex formulations did not cause platelet activation or blood cell hemolysis. Using the hamster cheek pouch in vivo model, the initial vasoactivity of GNP-Dex at concentrations (1-50 mg/ml) equivalent to the first pass of a bolus injection was a brief concentration-dependent dilation in arcade and terminal arterioles. However, they did not induce a pro-inflammatory endothelial dysfunction effect.

Differential expression patterns of CXCR3 variants and corresponding CXC chemokines in clear cell ovarian cancers and endometriosis.

OBJECTIVES: Carcinogenesis of the ovary is often associated with endometriosis. We previously demonstrated that antitumor chemokine receptor CXCR3 was upregulated both in endometriosis and ovarian cancers. Currently, little is known about the roles of CXCR3 variants in these ovarian diseases. In this study, we investigated the expression of CXCR3 variants and their corresponding ligands in endometriosis and ovarian cancers. METHODS: The expression patterns of CXCR3 variants (CXCR3A, CXCR3B and CXCR3-alt) and their corresponding ligands were investigated by quantitative RT-PCR, Western blot and in situ hybridization in normal ovaries (n=16), endometriosis (n=12), and clear cell ovarian cancers (n=22) including endometriosis-coexisting cases (n=11). RESULTS: Sequence analysis of purified RT-PCR products confirmed the presence of three CXCR3 variants in human ovaries. Quantitative RT-PCR analysis revealed differential expression patterns of these variants depending on conditions. CXCR3A was upregulated both in endometriosis and cancers. On the other hand, CXCR3-alt was upregulated and CXCR3B was downregulated in cancers compared with endometriosis. The corresponding ligand CXCL11 was upregulated only in the cancers with elevated CXCR3-alt. Another ligand CXCL4 was downregulated in the cancers with suppressed CXCR3B. In situ hybridization demonstrated preferential expression of CXCR3A in cancer cells and infiltrating lymphocytes. CXCR3B and CXCR3-alt were detectable mainly in microvessels. CONCLUSIONS: Collective data suggest that differential expression patterns of CXC chemokines and CXCR3 variants are involved in specific inflammatory microenvironment of ovarian cancers. Altered balance of CXCR3 variants may become helpful information for better understanding of the pathogenesis of ovarian cancers arising from endometriosis.

Expression of angiostatic platelet factor-4var/CXCL4L1 counterbalances angiogenic impulses of vascular endothelial growth factor, interleukin-8/CXCL8, and stromal cell-derived factor 1/CXCL12 in esophageal and colorectal cancer.

Chemokines influence tumor progression through regulation of leukocyte chemotaxis, angiogenesis, and metastasis. In this study, the regulated expression of angiogenic (stromal cell-derived factor [SDF]-1/CXCL12 and interleukin [IL]-8/CXCL8) and angiostatic (platelet factor [PF]-4var/CXCL4L1 and inducible protein [IP-10]/CXCL10) chemokines was examined in human colorectal and esophageal cancer. In HCT 116 and HCT-8 colorectal adenocarcinoma cells, the production of IL-8 immunoreactivity was up-regulated by IL-1beta, tumor necrosis factor (TNF)-alpha, the toll-like receptor (TLR) ligands double-stranded RNA and peptidoglycan and phorbol ester. Increased PF-4 and synergistic IL-8 and IP-10 induction in carcinoma cells after stimulation with IL-1beta plus TNF-alpha or interferon-gamma was demonstrated by enzyme-linked immunosorbent assay, quantitative reverse transcriptase polymerase chain reaction, or immunocytochemistry. In addition, IL-8 from HT-29 colorectal adenocarcinoma cells was molecularly identified as intact chemokine, as well as NH(2)-terminally truncated, more active IL-8(6-77). The presence of PF-4var, SDF-1, and vascular endothelial growth factor (VEGF) was evidenced by immunohistochemistry in surgical samples from 51 patients operated on for colon adenocarcinoma (AC), esophageal AC, or esophageal squamous cell carcinoma (SCC). PF-4var was strongly detected in colorectal cancer, whereas its expression in esophageal cancer was rather weak. Staining for SDF-1 was almost negative in esophageal SCC, whereas a more intense and frequent staining was observed in AC of the esophagus and colon. Staining for VEGF was moderately to strongly positive in all 3 types of cancer, although less prominent in esophageal AC. The heterogenous expression of angiogenic (IL-8, SDF-1) as well as angiostatic (IP-10, PF-4var) chemokines not only within the tumor and between the different cases but also between the different tumor cell types may indicate a distinct role of the various chemokines in the complex process of tumor development.

Expression of CXCL4 in microglia in vitro and in vivo and its possible signaling through CXCR3.

Signaling through chemokine receptor CXCR3 in the brain has been implicated in various brain diseases, as CXCR3 and its ligands are found under these conditions. Recently, a new chemokine ligand for CXCR3 was reported. In humans, an alternatively spliced variant of CXCR3 expressed on microvascular endothelial cells, named CXCR3b, was shown to bind CXCL4. In the periphery, the cellular expression and functions of CXCL4 are well described but in the brain its expression and function are unknown. Here, we show that brain microglia are a cellular source of CXCL4 in vitro and in vivo under neurodegenerating conditions. Microglial migration induced by CXCL4 is absent in CXCR3-deficient microglia, indicating a role of CXCR3. CXCL4 furthermore attenuates lipopolysaccharide-induced microglial phagocytosis and nitric oxide production in microglia and BV-2 cells. Based on these findings, it is proposed that locally released CXCL4 may control microglia responses.

Protein expression pattern in experimental pneumococcal meningitis.

In this study, we investigated cytokine expression during experimental pneumococcal meningitis. Mice were intracisternally infected with Streptococcus pneumoniae and treated with ceftriaxone starting at 24 h after infection. At different time points before and after antibiotic therapy, the cytokine expression pattern was determined in mouse brains using protein arrays. Underlining the power of this method, the meningitis-relevant cytokines interleukin-1beta (IL-1beta), IL-6, KC, macrophage inflammatory protein-2 (MIP-2), and monocyte chemoattractant protein-1 (MCP-1/CCL2) were markedly elevated in infected animals. Newly identified proteins during the acute stage of the disease (until 30 h after infection) included lymphotactin (XCL-1), MIP-1gamma (CCL9) and MCP-5 (CCL12), cytokine responsive gene- 2 (CRG-2/CXCL10) and CXCL16, and insulin-like growth factor binding protein 3 (IGFBP3). During later stages, an induction of T-cell activation-3 (TCA-3/CCL1), platelet factor-4 (PF-4/CXCL4) and stromal derived factor-1alpha (SDF-1alpha/CXCL13), and IL-4 was observed. The validity of this method was supported by an additional ELISA analysis of the expression profile of CXCL16 and IGFBP3, which was identical to that observed by protein array. In conclusion, the use of protein array technology led to an extension of the current picture of protein expression in pneumococcal meningitis. Most important, new factors that might play a role in pneumococcal meningitis were identified.

Platelet factor 4 gene transfection into tumor cells inhibits angiogenesis, tumor growth and metastasis.

Tumor growth and metastasis depend on angiogenesis, which is triggered by a chemical signal from the tumor cells to resting endothelial cells which then enter into a phase of rapid growth. Platelet Factor 4 (PF4) inhibits endothelial proliferation in vitro and angiogenesis in vivo. PF4 also inhibits tumor growth, however, as with other angiogenesis inhibitors, sustained tumor growth inhibition requires prolonged exposure to the recombinant protein. In this study, Lewis lung carcinoma (LLH) cells were transfected with the human PF4 via mammalian expression vectors and the ability of the transfected cells to form tumors and metastasis in vivo was evaluated. To evaluate the tumor growth rate of PF4-transfected (LLH/PF4) or control (LLH/neo) cells in vivo, we injected LLH/PF4 or LLH/neo cells subcutaneously (s.c.) or intravenously (i.v.). In the s.c. assay, LLH/PF4 had no significant effect on tumor growth. Conversely, in the i.v. assay, PF4 significantly reduced the number of lung metastasis (p=0.019) and weight (p=0.056). The inhibition of lung metastasis suggests that PF4 may inhibit tumor-associated neovascularization, and may prevent the affinity of tumor cells for the normal lung tissue.

Interleukin-32, CCL2, PF4F1 and GFD10 are the only cytokine/chemokine genes differentially expressed by in vitro cultured rheumatoid and osteoarthritis fibroblast-like synoviocytes.

Since cytokines and chemokines are important actors in rheumatoid arthritis (RA), the aim of this study was to compare the gene expression profiles in cultured fibroblast-like synoviocytes (FLS) obtained from patients with either RA, or osteoarthritis (OA), focusing our analysis on genes for cytokines and chemokines, and their respective receptors. Gene expression in cultured FLS (third passage) from eight patients with RA (RA-FLS) were compared with gene expression in cultured FLS from nine patients with OA (OA-FLS) using Affymetrix Human Genome U133 Plus 2.0 Array microarray, allowing analysis of over 54,000 transcripts. Among the 171 genes studied (241 probes), limiting the selection of differentially expressed genes to a significant value (p < 0.05), and a differential ratio of expression > 1.6, only four genes, namely IL-32, CCL2, PF4F1 and GDF10 were found to be differentially expressed. Out of these four genes, only higher expression of CCL2 has been reported previously in RA. The newly described cytokine IL-32 was the most prominently differentially expressed gene in the present study, with higher expression in RA-FLS than in OA-FLS (p < 0.0073). IL-32 might have a previously unidentified pivotal role in RA.

Combinatorial administration of molecules that simultaneously inhibit angiogenesis and invasion leads to increased therapeutic efficacy in mouse models of malignant glioma.

PURPOSE: We investigated the ability of the combinatorial administration of different inhibitors with activities on glioma angiogenesis, migration, and proliferation to produce a prolonged inhibition of glioma growth. EXPERIMENTAL DESIGN: We combined inhibitors affecting solely tumor angiogenesis (PF-4/CTF, cyclo-VEGI) or inhibitors affecting both angiogenesis and invasion together (PEX, PF-4/DLR). RESULTS: When administered in combination, these drugs produced a prolonged and increased inhibition of glioma growth independently from the type of inhibitor used. The combinatory administration was more effective than the administration of a single inhibitor alone, and a strong therapeutic response was reached with a significantly lower amount of protein. The strongest inhibition was observed when human PEX and PF-4/DLR, which affect both glioma angiogenesis and invasion by separate mechanisms, were combined. CONCLUSIONS: This supports the concept that prolonged glioma growth inhibition can be achieved by simultaneous delivery of molecules that target both tumor and endothelial cells and acting by separate mechanisms.

[The effects of culture supernatant of human GRC-1 cells transfected with PF4 cDNA on the VEGF expression and the growth of ECV304 cells].

AIM: To construct the eukaryotic expression vector pcDNA3-PF4-SS, and to detect the effects of the culture supernatant of transfected GRC-1 cells on the VEGF expression in transfected GRC-1 cells and the growth of ECV304 cells. METHODS: The eukaryotic expression vector pcDNA3-PF4-SS was constructed and identified with Bgl II/BamH I digestion. The pcDNA3-PF4-SS was transfected stably into GRC-1 cells with lipofectamine mediation. The VEGF expression in transfected GRC-1 cells was detected by immunohistochemical staining, and the effect of the culture supernatant of transfected GRC-1 cells on ECV304 cells was detected by MTT colorimetry. RESULTS: Restrictive enzyme (Bgl II/BamH I)digestion analysis showed that the recombinant expression vector pcDNA3-PF4-SS had been constructed successfully. RT-PCR detection proved that hPF4 cDNA had been transfected into GRC-1 cells. The result of immunohistochemical staining showed that the VEGF expression could be seen in the cytoplasm and on cytomembrane of GRC-1 cells transfected with pcDNA3-PF4-SS, but the expression obviously weakened as comparison with that before transfection. Cell counting and MTT colorimetry manifested that the culture supernatant of transfected GRC-1 cells could inhibit markedly growth of ECV304 cells. CONCLUSION: The eukaryotic expression vector pcDNA3-PF4-SS has been constructed successfully, and stably transfected into the GRC-1 cells. The culture supernatant of transfected GRC-1 cells has obviously inhibitory effect on the growth of ECV304 cells and the VEGF expression in the GRC-1 cells, which lays some foundation for exploring the mechanism for anti-tumor growth and developing tumor vaccine for kidney neoplasms.

Properties of ets-1 binding to chromatin and its effect on platelet factor 4 gene expression.

Ets-1 is important for transcriptional regulation in several hematopoietic lineages, including megakaryocytes. Some transcription factors bind to naked DNA and chromatin with different affinities, while others do not. In the present study we used the megakaryocyte-specific promoters platelet factor 4 (PF4), and glycoprotein IIb (GPIIb) as model systems to explore the properties of Ets-1 binding to chromatin. Chromatin immunoprecipitation assays indicated that Ets-1 binds to proximal regions in the PF4 and GPIIb promoters in vivo. In vitro and in vivo experiments showed that Ets-1 binding to chromatin on lineage-specific promoters does not require lineage-specific factors. Moreover, this binding shows the same order of affinity as the binding to naked DNA and does not require ATP-dependent or Sarkosyl-sensitive factors. The effect of Ets-1 binding on promoter activity was examined using the PF4 promoter as a model. We identified a novel Ets-1 site (at -50), and a novel Sarkosyl-sensitive DNase I-hypersensitive site generated by Ets-1 binding to chromatin, which significantly affect PF4 promoter activity. Taken together, our results suggest a model by which Ets-1 binds to chromatin without the need for lineage-specific accessory factors, and Ets-1 binding induces changes in chromatin and affects transactivation, which are essential for PF4 promoter activation.

Platelet activity measured by plasma levels of beta-thromboglobulin and platelet factor 4 in seasonal allergic rhinitis during natural pollen exposure.

BACKGROUND: Upon activation, platelets release mediators with potent inflammatory properties in IgE-mediated immune responses. Moreover, the atopic state leads towards functional abnormalities of these cells. OBJECTIVE: The aim of our study was to examine the degree of activation of circulating platelets in patients with seasonal allergic rhinitis (SAR) during the symptomatic period, to improve the understanding of platelet function in atopy. SUBJECTS AND METHOD: Plasma levels of beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4) - specific markers of platelet activation were measured by enzyme-linked immunoassay in 20 patients suffering from SAR and in 15 healthy, nonatopic subjects. RESULTS: There were no significant differences in peripheral blood platelet numbers and plasma levels of beta-TG and PF4 in SAR patients when compared with control subjects. CONCLUSION: It seems that increased in vivo platelet activity, assessed by measuring plasma beta-TG and PF4, may not occur during allergic inflammation that is associated with SAR.

PREP1, MEIS1 homolog protein, regulates PF4 gene expression.

We have previously demonstrated that homeodomain proteins, MEIS1 and PBXs, transactivate the PF4 gene through the novel regulatory element termed TME. This study focuses on Pbx regulating protein 1 (PREP1), a MEIS1 homolog protein, for its transcriptional activity in the PF4 promoter. PREP1 binds to the TME in HEL cells. PREP1 was expressed in human megakaryocytes that differentiated from CD34(+) cells. EMSA shows that either PREP1 by itself or PREP1/PBX complexes bind to the two TGACAG motifs in the TME and activate the PF4 promoter. Furthermore, PREP1 and PREP1/PBX complexes synergistically activate the PF4 promoter with GATA-1 and ETS-1. These data demonstrate that PREP1 is also an important transcription factor that regulates PF4 gene expression such as MEIS1. Additionally, these data imply functional similarities and differences between PREP1 and MEIS1 in the regulation of PF4 gene expression.

Comparative antithrombotic potencies of direct thrombin inhibitors and low-molecular-weight heparins in an ex vivo human experimental thrombosis model.

Direct thrombin inhibitors (DTIs) such as hirudins and melagatran are currently developed for antithrombotic therapy. They should possess some advantages over the currently used low-molecular-weight heparins (LMWHs). They may also act through an inhibition of thrombin-induced platelet activation. The antithrombotic effects of DTIs and of LMWHs were investigated in an ex vivo thrombosis model with human blood in order to analyze the inhibition of thrombin-antithrombin as well as the platelet factor 4 formation. The data show that DTIs inhibit both fibrin formation and platelet activation, which is of clinical relevance especially for melagatran.

Increased plasma thrombospondin-1 (TSP-1) levels are associated with the TNF alpha-308A allele in children with juvenile dermatomyositis.

Vascular occlusion is more frequent in children with juvenile dermatomyositis (JDM) who have the TNF alpha-308A allele. One of the potent anti-angiogenic factors is thrombospondin-1 (TSP-1). This study investigated the association of the TNF alpha-308A allele with circulating levels of angiogenic mediators, TSP-1, and platelet factor 4 (PF4) using fresh, platelet-poor plasma (PPP). The TNF alpha-308A allele was characterized by PCR amplification and NcoI digestion. Concentrations of TSP-1 and PF4 in PPP from 31 JDM patients and 25 matched pediatric controls were determined by ELISA. The majority of the JDM children with the TNF alpha-308A allele (7/12) produced more TSP-1 than their TNF alpha-308G counterparts (P < 0.05), and their TSP-1 values were inversely related to those for PF4 (P < 0.0006). We conclude that the increased circulating concentrations of TSP-1 associated with the TNF alpha-308A allele suggest that this anti-angiogenic regulator may play a significant role in the augmented vascular occlusion observed in JDM children with this genetic marker.