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Parker ZF, Rux AH, Riblett AM, Lee FH, Rauova L, Cines DB, Poncz M, Sachais BS, Doms RW. Platelet Factor 4 Inhibits and Enhances HIV-1 Infection in a Concentration-Dependent Manner by Modulating Viral Attachment. AIDS Res Hum Retroviruses 2016; 32:705-17. [PMID: 26847431 DOI: 10.1089/aid.2015.0344] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Platelet factor 4 (PF4) has been recently shown to inhibit infection by a broad range of human immunodeficiency virus type 1 (HIV-1) isolates in vitro. We found that the inhibitory effects of PF4 are limited to a defined concentration range where PF4 exists largely in a monomeric state. Under these conditions, PF4 bound the HIV-1 envelope protein and inhibited HIV-1 attachment to the cell surface. However, as concentrations increased to the point where PF4 exists largely in tetrameric or higher-order forms, viral infection in vitro was enhanced. Enhancement could be inhibited by mutations in PF4 that shift the oligomeric equilibrium toward the monomeric state, or by using soluble glycosaminoglycans (GAGs) to which tetrameric PF4 avidly binds. We conclude that at physiologically relevant concentrations, oligomeric PF4 enhances infection by HIV-1 by interacting with the viral envelope protein as well as cell surface GAGs, enhancing virus attachment to the cell surface. This effect was not specific to HIV-1, as enhancement was seen with some but not all other viruses tested. The biphasic effects of PF4 on HIV-1 infection suggest that native PF4 will not be a useful antiviral agent and that PF4 could contribute to the hematologic abnormalities commonly seen in HIV-infected individuals by enhancing virus infection in the bone marrow.
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Karafin MS, Sachais BS, Connelly-Smith L, Field JJ, Linenberger ML, Padmanabhan A. NHLBI state of the science symposium in therapeutic apheresis: Knowledge gaps and research opportunities in the area of hematology-oncology. J Clin Apher 2015; 31:38-47. [DOI: 10.1002/jca.21400] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Accepted: 04/06/2015] [Indexed: 01/19/2023]
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Farooqi MS, Lai Y, Lancaster E, Schmitt SE, Sachais BS. Therapeutic plasma exchange and immunosuppressive therapy in a patient with anti-GAD antibody-related epilepsy: quantification of the antibody response. J Clin Apher 2014; 30:8-14. [PMID: 24961613 DOI: 10.1002/jca.21342] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Revised: 05/26/2014] [Accepted: 06/05/2014] [Indexed: 11/09/2022]
Abstract
Antibodies to glutamic acid decarboxylase (GAD) have been associated with a host of neurological disorders including stiff person syndrome, cerebellar ataxia, limbic encephalitis, and epilepsy. Whether anti-GAD antibodies have an etiological role in these neurological disorders or simply serve as disease markers is unclear. Here, we report a case of a patient with recurrent seizures, poorly responsive to conventional treatment, associated with anti-GAD antibodies. The patient was experiencing near daily seizures at the time of presentation and had marked improvement while receiving immunosuppressive therapy and therapeutic plasma exchange (TPE). We go on to show that the patient had a substantial reduction of her GAD autoantibody burden following this therapy. Using immunostaining, we further demonstrate a progressive loss of GAD reactivity in the patient's sera to neurons and GAD-expressing HELA cells with successive TPEs. Hence, these data support the concept of an immune-mediated pathogenic component to these autoantibody-associated neurological syndromes.
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Cho MJ, Lo ASY, Mao X, Nagler AR, Ellebrecht CT, Mukherjee EM, Hammers CM, Choi EJ, Sharma PM, Uduman M, Li H, Rux AH, Farber SA, Rubin CB, Kleinstein SH, Sachais BS, Posner MR, Cavacini LA, Payne AS. Shared VH1-46 gene usage by pemphigus vulgaris autoantibodies indicates common humoral immune responses among patients. Nat Commun 2014; 5:4167. [PMID: 24942562 PMCID: PMC4120239 DOI: 10.1038/ncomms5167] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Accepted: 05/20/2014] [Indexed: 12/13/2022] Open
Abstract
Pemphigus vulgaris (PV) is a potentially fatal blistering disease caused by autoantibodies (autoAbs) against desmoglein 3 (Dsg3). Here, we clone anti-Dsg3 antibodies (Abs) from four PV patients and identify pathogenic VH1-46 autoAbs from all four patients. Unexpectedly, VH1-46 autoAbs had relatively few replacement mutations. We reverted antibody somatic mutations to their germline sequences to determine the requirement of mutations for autoreactivity. Three of five VH1-46 germline-reverted Abs maintain Dsg3 binding, compared with zero of five non-VH1-46 germline-reverted Abs. Site-directed mutagenesis of VH1-46 Abs demonstrates that acidic amino-acid residues introduced by somatic mutation or heavy chain VDJ recombination are necessary and sufficient for Dsg3 binding. Our data suggest that VH1-46 autoantibody gene usage is commonly found in PV because VH1-46 Abs require few to no mutations to acquire Dsg3 autoreactivity, which may favour their early selection. Common VH gene usage indicates common humoral immune responses, even among unrelated patients.
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Litvinov RI, Yarovoi SV, Rauova L, Barsegov V, Sachais BS, Rux AH, Hinds JL, Arepally GM, Cines DB, Weisel JW. Distinct specificity and single-molecule kinetics characterize the interaction of pathogenic and non-pathogenic antibodies against platelet factor 4-heparin complexes with platelet factor 4. J Biol Chem 2013; 288:33060-70. [PMID: 24097975 DOI: 10.1074/jbc.m113.481598] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Heparin-induced thrombocytopenia (HIT) is a thrombotic complication of heparin therapy mediated by antibodies to complexes between platelet factor 4 (PF4) and heparin or cellular glycosaminoglycans. However, only a fraction of patients with anti-PF4-heparin antibodies develop HIT, implying that only a subset of these antibodies is pathogenic. The basis for the pathogenic potential of anti-PF4-heparin antibodies remains unclear. To elucidate the intrinsic PF4-binding properties of HIT-like monoclonal antibody (KKO) versus non-pathogenic antibody (RTO) at the single-molecule level, we utilized optical trap-based force spectroscopy to measure the strength and probability of binding of surface-attached antibodies with oligomeric PF4 to simulate interactions on cells. To mimic the effect of heparin in bringing PF4 complexes into proximity, we chemically cross-linked PF4 tetramers using glutaraldehyde. Analysis of the force histograms revealed that KKO-PF4 interactions had ∼10-fold faster on-rates than RTO-PF4, and apparent equilibrium dissociation constants differed ∼10-fold with similar force-free off-rates (k(off) = 0.0031 and 0.0029 s(-1)). Qualitatively similar results were obtained for KKO and RTO interacting with PF4-heparin complexes. In contrast to WT PF4, KKO and RTO showed lower and similar binding probabilities to cross-linked PF4(K50E), which forms few if any oligomers. Thus, formation of stable PF4 polymers results in much stronger interactions with the pathogenic antibody without a significant effect on the binding of the non-pathogenic antibody. These results suggest a fundamental difference in the antigen-binding mechanisms between model pathogenic and non-pathogenic anti-PF4 antibodies that might underlie their distinct pathophysiological behaviors.
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Callan MB, Patel RT, Rux AH, Bandyopadhyay S, Sireci AN, O'Donnell PA, Ruane T, Sikora T, Marryott K, Sachais BS, Hod EA. Transfusion of 28-day-old leucoreduced or non-leucoreduced stored red blood cells induces an inflammatory response in healthy dogs. Vox Sang 2013; 105:319-27. [PMID: 23763639 DOI: 10.1111/vox.12058] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2013] [Revised: 04/16/2013] [Accepted: 04/26/2013] [Indexed: 01/24/2023]
Abstract
BACKGROUND AND OBJECTIVES Studies in mice suggest that rapid transfusions of red blood cells (RBCs), refrigerator stored for longer durations, induce a pro-inflammatory cytokine response. Studies in human neonates confirm these findings; however, to date, adult human studies have failed to replicate these findings. We used healthy research dogs to begin to examine the factors affecting the cytokine response to transfusion. MATERIALS AND METHODS In a prospective study, healthy dogs were randomized for two autologous packed RBC transfusions after 7 (i.e. 'fresh') and 28 (i.e. 'old') days of storage, or after 28 and 7 days of storage, with or without prestorage leucoreduction (LR). RESULTS No significant differences were observed between LR and non-LR transfusions for all circulating analytes measured following transfusion. A pro-inflammatory cytokine response, exemplified by monocyte chemoattractant protein-1, was observed 6 h after only old RBC transfusions, irrespective of infusion rate (P < 0·001). This response was accompanied by increased neutrophil counts (P < 0·001) and decreased platelet counts (P < 0·001). CONCLUSION In healthy dogs, old RBC transfusions induce inflammation, which is unaffected by infusion rate.
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Tanhehco YC, Cuker A, Rudnick M, Sachais BS. Investigation of a potential protective mechanism against heparin-induced thrombocytopenia in patients on chronic intermittent hemodialysis. Thromb Res 2013; 131:244-8. [PMID: 23305841 DOI: 10.1016/j.thromres.2012.12.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2012] [Revised: 11/16/2012] [Accepted: 12/15/2012] [Indexed: 11/19/2022]
Abstract
BACKGROUND Heparin-induced thrombocytopenia (HIT) develops as a result of platelet (PLT) activation by anti-platelet factor 4 (PF4)/heparin complex antibodies. Despite repeated exposure to heparin, patients undergoing chronic intermittent hemodialysis (HD) rarely develop HIT. We investigated the possibility that HD decreases/removes PF4 from PLT surfaces and/or plasma, thereby disfavoring immune complex formation as a mechanism of protection against HIT. MATERIALS AND METHODS We enrolled 20 patients undergoing chronic HD at the Penn Presbyterian Medical Center. Blood samples were drawn before, during and after treatment in the presence and absence of heparin. PF4, anti-PF4/heparin antibody, heparin, and P-selectin levels were measured. RESULTS No patients demonstrated clinical symptoms of HIT. PLT surface PF4 levels decreased and plasma PF4 levels increased concurrently with the increase in plasma heparin concentration. In the absence of heparin, PLT surface and plasma PF4 levels were unchanged. Anti-PF4/heparin antibodies, which were non-functional by the serotonin release assay, were detectable in 8 patients. PLT surface P-selectin levels did not change during treatment. CONCLUSIONS Removal of PLT surface and/or plasma PF4 as a mechanism of protection against HIT in patients undergoing HD is not supported by the results of our study, although the transient decrease in PLT surface PF4 in the presence of large amounts of heparin remains a candidate mechanism. The small sample size, single type of dialyzer membrane, and early sampling time points may have led to the inability to detect changes in PF4 levels. Future studies should explore other potential protective mechanisms.
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Marshall CS, Andrzejewski C, Carey PM, Crookston KP, Li Y, Lopez-Plaza I, Sachais BS, Schwartz J, Winters JL, Wong ECC, Wu Y. Milestones for Apheresis education. J Clin Apher 2012; 27:242-6. [DOI: 10.1002/jca.21235] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Accepted: 05/23/2012] [Indexed: 11/11/2022]
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Tanhehco YC, Rux AH, Sachais BS. Low-density lipoprotein apheresis reduces platelet factor 4 on the surface of platelets: a possible protective mechanism against heparin-induced thrombocytopenia and thrombosis. Transfusion 2010; 51:1022-9. [PMID: 20977482 DOI: 10.1111/j.1537-2995.2010.02911.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BACKGROUND Heparin-induced thrombocytopenia and thrombosis (HITT) is characterized by thrombocytopenia due to the formation of antibodies against heparin : platelet factor 4 (PF4) complexes. Despite the exposure to heparin during treatment and predisposition of patients with atherosclerosis to HITT, HITT in patients undergoing low-density lipoprotein (LDL) apheresis is rare. We investigated the possibility that LDL apheresis decreases PF4 on platelet (PLT) surfaces and/or plasma HITT antibody levels, either of which would disfavor HITT. STUDY DESIGN AND METHODS We enrolled 25 patients undergoing LDL apheresis at the Hospital of the University of Pennsylvania. Blood samples were drawn before and after treatment. Plasma samples were drawn proximal and distal to the LA-15 treatment column. PF4, HITT antibodies, heparin levels, and P-selectin were measured. RESULTS No patient had clinical symptoms of HITT. The LA-15 column was found to efficiently remove PF4. PF4 levels in peripheral blood plasma did not change significantly after LDL apheresis. However, PLT surface PF4 significantly decreased after treatment. HITT antibodies were found in only two patients and were nonfunctional. PLT surface P-selectin did not change during treatment. CONCLUSIONS We have demonstrated that LDL apheresis via dextran sulfate absorption removes plasma PF4 and reduces the amount of PF4 on the surface of circulating PLTs. Reduced surface PF4 may decrease antibody formation and/or recognition by HITT antibodies. These data provide a potential explanation for the near lack of HITT in hypercholesterolemic patients undergoing LDL apheresis. They also suggest the possibility that LDL apheresis using dextran sulfate adsorption may have therapeutic value in the treatment of HITT.
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Adamski J, Griffin AC, Eisenmann C, Milone MC, Sachais BS. Increased risk of citrate reactions in patients with multiple myeloma during peripheral blood stem cell leukapheresis. J Clin Apher 2010; 25:188-94. [PMID: 20818713 DOI: 10.1002/jca.20235] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The citrate based anticoagulant ACD is commonly used in apheresis procedures. Due to its ability to decrease ionized calcium, citrate may cause unpleasant symptoms, such as paresthesias and muscle cramps, in patients undergoing therapeutic and donor apheresis. We noticed that patients with multiple myeloma (MM) undergoing autologous stem cell leukapheresis appeared to have more citrate reactions when compared to other patients undergoing the same procedure. A retrospective chart review was performed to evaluate 139 (of 151) consecutive patients with MM, amyloidosis, hematological and solid malignancies who had autologous peripheral blood stem cell collection between January 2007 and February 2008. Citrate reactions, ranging from mild (e.g., perioral tingling and parasthesias) to severe (e.g., nausea/vomiting and muscle cramps) were noted for 35 patients. Twenty-three of 63 patients with MM had documented citrate reactions, which was significantly higher than those with other hematological and solid malignancies (37% vs. 20%; P < 0.05, Relative Risk (RR) = 1.9). The severities of citrate reactions were the same in both groups; approximately 50% of patients in each group received i.v. calcium gluconate for treatment of hypocalcemia. No correlation between bisphosphonate therapy and citrate reactions were noted in our study group. Examination of available laboratory values related to calcium homeostasis, liver, and renal function failed to reveal a mechanism for the increase in citrate reactions observed. In summary, this single institution retrospective study indicates that patients with MM are more sensitive to citrate-induced hypocalcemia during leukapheresis when compared to patients with other hematological and solid malignancies. Strategies for decreasing citrate reactions (e.g., supplemental calcium and slowing return rates) should be considered for patient safety and comfort, especially in the MM population, on a prophylactic rather than reactive basis.
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Adamski J, Jamensky L, Ross J, Siegel DL, Sachais BS. Anaphylactoid-like reactions in a patient with HyperLp(a)lipidemia undergoing LDL apheresis with dextran sulfate adsorption and herbal therapy with the spice turmeric. J Clin Apher 2010; 25:354-7. [DOI: 10.1002/jca.20254] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2010] [Accepted: 06/18/2010] [Indexed: 01/09/2023]
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Roback JD, Caldwell S, Carson J, Davenport R, Drew MJ, Eder A, Fung M, Hamilton M, Hess JR, Luban N, Perkins JG, Sachais BS, Shander A, Silverman T, Snyder E, Tormey C, Waters J, Djulbegovic B. Evidence-based practice guidelines for plasma transfusion. Transfusion 2010; 50:1227-39. [PMID: 20345562 DOI: 10.1111/j.1537-2995.2010.02632.x] [Citation(s) in RCA: 199] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
BACKGROUND There is little systematically derived evidence-based guidance to inform plasma transfusion decisions. To address this issue, the AABB commissioned the development of clinical practice guidelines to help direct appropriate transfusion of plasma. STUDY DESIGN AND METHODS A systematic review (SR) and meta-analysis of randomized and observational studies was performed to quantify known benefits and harms of plasma transfusion in common clinical scenarios (see accompanying article). A multidisciplinary guidelines panel then used the SR and the GRADE methodology to develop evidence-based plasma transfusion guidelines as well as identify areas for future investigation. RESULTS Based on evidence ranging primarily from moderate to very low in quality, the panel developed the following guidelines: 1) The panel suggested that plasma be transfused to patients requiring massive transfusion. However, 2) the panel could not recommend for or against transfusion of plasma at a plasma : red blood cell ratio of 1:3 or more during massive transfusion, 3) nor could the panel recommend for or against transfusion of plasma to patients undergoing surgery in the absence of massive transfusion. 4) The panel suggested that plasma be transfused in patients with warfarin therapy-related intracranial hemorrhage, 5) but could not recommend for or against transfusion of plasma to reverse warfarin anticoagulation in patients without intracranial hemorrhage. 6) The panel suggested against plasma transfusion for other selected groups of patients. CONCLUSION We have systematically developed evidence-based guidance to inform plasma transfusion decisions in common clinical scenarios. Data from additional randomized studies will be required to establish more comprehensive and definitive guidelines for plasma transfusion.
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Sachais BS, Turrentine T, Dawicki McKenna JM, Rux AH, Rader D, Kowalska MA. Elimination of platelet factor 4 (PF4) from platelets reduces atherosclerosis in C57Bl/6 and apoE-/- mice. Thromb Haemost 2007; 98:1108-1113. [PMID: 18000617] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Activated platelets, which release platelet factor 4 (PF4) are present in patients with atherosclerosis. To date, no direct in-vivo evidence exists for the involvement of PF4 in atherogenesis. In the current study, we tested the hypothesis that PF4 is atherogenic, and that genetic elimination of PF4 would protect mice from atherosclerosis. We have bred PF4(-/-) mice onto two athero-susceptible backgrounds, WT-C57Bl/6(WT) and apoE(-/-) to examine the importance of PF4 in atherogenesis. In order to induce atherosclerosis, WT and PF4(-/-) mice were fed an atherogenic diet for 30 weeks, while apoE(-/-) and apoE(-/-) PF4(-/-) mice were fed a high-fat Western-style diet for 10 weeks. Examination of lesions in the aortic roots of atherogenic diet fed mice demonstrated reduced atherosclerosis in PF4(-/-) (20% compared to WT). Examination of apoE(-/-) mice demonstrated similar changes, with apoE(-/-) PF4(-/-) mice demonstrating 37% of the aortic atherosclerotic burden compared to apoE(-/-) mice. Although we found similar levels of total and non-HDL cholesterol in WT and PF4(-/-) mice, HDL-cholesterol levels were increased in PF4(-/-) on both backgrounds. These data demonstrate, for the first time, that the platelet specific chemokine PF4 promotes atherosclerotic lesion development in vivo.
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Zhang P, Pan W, Rux AH, Sachais BS, Zheng XL. The cooperative activity between the carboxyl-terminal TSP1 repeats and the CUB domains of ADAMTS13 is crucial for recognition of von Willebrand factor under flow. Blood 2007; 110:1887-94. [PMID: 17540842 PMCID: PMC1976376 DOI: 10.1182/blood-2007-04-083329] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2007] [Accepted: 05/29/2007] [Indexed: 01/06/2023] Open
Abstract
ADAMTS13 cleaves von Willebrand factor (VWF) between Tyr(1605) and Met(1606) residues at the central A2 subunit. The amino-terminus of ADAMTS13 protease appears to be sufficient to bind and cleave VWF under static and denatured condition. However, the role of the carboxyl-terminus of ADAMTS13 in substrate recognition remains controversial. Present study demonstrates that ADAMTS13 cleaves VWF in a rotation speed- and protease concentration-dependent manner on a mini vortexer. Removal of the CUB domains (delCUB) or truncation after the spacer domain (MDTCS) significantly impairs its ability to cleave VWF under the same condition. ADAMTS13 and delCUB (but not MDTCS) bind VWF under flow with dissociation constants (K(D)) of about 50 nM and about 274 nM, respectively. The isolated CUB domains are neither sufficient to bind VWF detectably nor capable of inhibiting proteolytic cleavage of VWF by ADAMTS13 under flow. Addition of the TSP1 5-8 (T5-8CUB) or TSP1 2-8 repeats (T2-8CUB) to the CUB domains restores the binding affinity toward VWF and the inhibitory effect on cleavage of VWF by ADAMTS13 under flow. These data demonstrate directly and quantitatively that the cooperative activity between the middle carboxyl-terminal TSP1 repeats and the distal carboxyl-terminal CUB domains may be crucial for recognition and cleavage of VWF under flow.
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Abstract
Thrombosis is an important clinical entity, and pathologic thrombosis, in the form of atherosclerosis, is a major cause of morbidity and mortality. Recent research points to the role of chemokines, normally key factors in inflammation, in thrombogenesis. Many recent studies in murine transgenic and knockout models show that chemokines and their receptors are important modulators of the process of thrombus formation, particularly in atherosclerosis. Platelet-released chemokines can potentiate or inhibit thrombosis and inflammation. This review focuses on the role of chemokines in platelet activation and thrombosis, particularly as it relates to atherosclerosis. Further studies to define this complex interaction are underway.
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Cines DB, Rauova L, Arepally G, Reilly MP, McKenzie SE, Sachais BS, Poncz M. Heparin-induced thrombocytopenia: An autoimmune disorder regulated through dynamic autoantigen assembly/disassembly. J Clin Apher 2007; 22:31-6. [PMID: 17285619 DOI: 10.1002/jca.20109] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Heparin-induced thrombocytopenia (HIT) is the most common drug-induced, antibody-mediated cause of thrombocytopenia and thrombosis. HIT is caused by IgG antibodies that bind to epitopes on platelet factor 4 (PF4) released from activated platelets that develop when it forms complexes with heparin. Anti-PF4/antibodies develop in over 50% of patients undergoing surgery involving cardiopulmonary bypass (CPB), an incidence 20-fold higher than HIT. Why might this occur? Binding of HIT IgG occurs only over a narrow molar ratio of reactants, being optimal at 1 mol PF4 tetramer to 1 mol unfractionated heparin (UFH). At these ratios, PF4 and UFH form ultralarge (>670 kD) complexes that bind multiple IgG molecules/complex, are highly antigenic, and promote platelet activation. Low molecular weight heparin (LMWH), which is less antigenic, forms ultralarge complexes less efficiently and largely at supratherapeutic concentrations. In transgenic mice that vary in expression of human PF4 on their platelets, antigenic complexes form between PF4 and endogenous chondroitin sulfate. Binding of HIT IgG to platelets and induction of thrombocytopenia in vivo is proportional to PF4 expression. Heparin prolongs the duration and exacerbates the severity of the thrombocytopenia. High doses of heparin, as used in CPB, or protamine, which competes with PF4 for heparin, disrupts antigen formation and prevents thrombocytopenia induced by HIT antibody. These studies may help explain the disparity between the incidence of antibody formation and clinical disease and may help identify patients at risk for HIT (high platelet PF4). They also demonstrate that this autoimmune disease can be modulated at the level of autoantigen formation and point to rational means to intervene proximal to thrombin generation.
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Reilly MP, Taylor SM, Franklin C, Sachais BS, Cines DB, Williams KJ, McKenzie SE. Prothrombotic factors enhance heparin-induced thrombocytopenia and thrombosis in vivo in a mouse model. J Thromb Haemost 2006; 4:2687-94. [PMID: 16961586 DOI: 10.1111/j.1538-7836.2006.02201.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BACKGROUND Heparin-induced thrombocytopenia/thrombosis (HIT/T) is a common cause of life- and limb-threatening thrombosis. The development of antibodies that react with complexes of heparin and platelet factor 4 (PF4) is fundamental to the development of the disease. However, anti-PF4/heparin antibodies are far more common than is HIT/T and there is less understanding of the factors that contribute to thrombosis in only a subset of patients. OBJECTIVES Both qualitative and quantitative differences in multiple factors (e.g. antibodies, heparin and platelets) may influence the clinical course of patients who develop anti-PF4/heparin antibodies. We examined the hypothesis that host-specific factors, such as comorbid prothrombotic conditions, would exacerbate the pathologic effects of anti-PF4/heparin antibodies. METHODS AND RESULTS A mouse model transgenic for human Fcgamma RIIa and PF4 and null for mouse PF4 was used to study the influence of prothrombotic conditions on the effects of anti-PF4/heparin antibodies in vivo. To simulate a prothrombotic milieu, mice were fed a hypercholesterolemic diet (HD). HD-fed mice had elevated plasma cholesterol, increased platelet reactivity and increased endothelial activation relative to mice fed a standard diet (SD). Age- and sex-matched mice from each diet group were treated with an anti-PF4/heparin antibody and heparin. HD-fed mice developed more severe thrombocytopenia than similarly treated SD-fed mice. Mice with moderate to severe thrombocytopenia had elevated plasma levels of thrombin-antithrombin complexes, indicative of increased thrombin generation in vivo. Platelet-fibrin thrombi were observed in multiple organs of HD-fed mice that developed severe thrombocytopenia. CONCLUSIONS Host-specific factors, such as prothrombotic changes in platelet reactivity and/or endothelial activation, may influence the development of thrombosis in a subset of patients who develop anti-PF4/heparin antibodies.
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Suvarna S, Rauova L, McCracken EKE, Goss CM, Sachais BS, McKenzie SE, Reilly MP, Gunn MD, Cines DB, Poncz M, Arepally G. PF4/heparin complexes are T cell-dependent antigens. Blood 2005; 106:929-31. [PMID: 15845897 PMCID: PMC1895158 DOI: 10.1182/blood-2004-12-4955] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2005] [Accepted: 03/25/2005] [Indexed: 01/05/2023] Open
Abstract
Heparin-induced thrombocytopenia (HIT) is a life-threatening, thrombotic disorder associated with development of anti-platelet factor 4 (anti-PF4)/heparin autoantibodies. Little is known about the antigenic and cellular requirements that initiate the immune response to these complexes. To begin to delineate mechanisms of autoantibody formation in HIT, we studied the immunizing effects of murine PF4 (mPF4)/heparin in mice with and without thymic function. Euthymic mice were injected with mPF4/heparin complexes, mPF4, heparin, or buffer. Mice injected with mPF4/heparin, but not mPF4 or heparin alone, developed heparin-dependent autoantibodies that shared serologic and functional characteristics of human HIT antibodies, including preferential binding to mPF4/heparin complexes and causing heparin- and FcRgammaIIA-dependent platelet activation. In contrast, athymic mice did not develop HIT-like antibodies. Taken together, these studies establish that PF4/heparin complexes are highly immunogenic and elicit self-reacting anti-PF4/heparin antibodies in a T cell-dependent manner.
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Sachais BS, Katz J, Ross J, Rader DJ. Long-term effects of LDL apheresis in patients with severe hypercholesterolemia. J Clin Apher 2005; 20:252-5. [PMID: 15880364 DOI: 10.1002/jca.20036] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Familial hypercholesterolemia (FH) is an inherited disorder of lipoprotein metabolism involving mutations in the LDL receptor (LDL-R). Patients with mutation in one (heterozygous) or both (homozygous) genes have markedly elevated LDL cholesterol and are at increased risk for coronary heart disease (CHD). Aggressive lipid lowering is required for homozygous and many heterozygous FH patients. This often involves LDL-apheresis, where LDL and other apo-B containing lipoproteins are selectively removed from the plasma. We have retrospectively studied 34 patients treated with biweekly LDL-apheresis at the Hospital of the University of Pennsylvania. In our patient population, adverse events were uncommon and rarely resulted in shortened treatment time. There was a dramatic decrease in the relative risk of cardiovascular events and cardiovascular interventions in patients treated with LDL-apheresis for an average of 2.5 years. Some but not all patients had long-term reduction in their LDL levels as a result of LDL-apheresis, suggesting that time-averaged reduction in LDL and/or LDL:HDL ratios were responsible for clinical improvement. These data support the use of LDL-apheresis in patients with FH, as well as medication-intolerant patients that have elevated LDL cholesterol despite maximal pharmacological treatment.
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Yu G, Rux AH, Ma P, Bdeir K, Sachais BS. Endothelial expression of E-selectin is induced by the platelet-specific chemokine platelet factor 4 through LRP in an NF-kappaB-dependent manner. Blood 2004; 105:3545-51. [PMID: 15591119 PMCID: PMC1895024 DOI: 10.1182/blood-2004-07-2617] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The involvement of platelets in the pathogenesis of atherosclerosis has recently gained much attention. Platelet factor 4 (PF4), a platelet-specific chemokine released on platelet activation, has been localized to atherosclerotic lesions, including macrophages and endothelium. In this report, we demonstrate that E-selectin, an adhesion molecule involved in atherogenesis, is up-regulated in human umbilical vein endothelial cells exposed to PF4. Induction of E-selectin RNA is time and dose dependent. Surface expression of E-selectin, as measured by flow cytometry, is also increased by PF4. PF4 induces E-selectin expression by activation of transcriptional activity. Activation of nuclear factor-kappaB is critical for PF4-induced E-selectin expression, as demonstrated by promoter activation studies and electrophoretic mobility shift assays. Further, we have identified the low-density lipoprotein receptor-related protein as the cell surface receptor mediating this effect. These results demonstrate that PF4 is able to increase expression of E-selectin by endothelial cells and represents another potential mechanism by which platelets may participate in atherosclerotic lesion progression.
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Pitsilos S, Hunt J, Mohler ER, Prabhakar AM, Poncz M, Dawicki J, Khalapyan TZ, Wolfe ML, Fairman R, Mitchell M, Carpenter J, Golden MA, Cines DB, Sachais BS. Platelet factor 4 localization in carotid atherosclerotic plaques: correlation with clinical parameters. Thromb Haemost 2004; 90:1112-20. [PMID: 14652645 DOI: 10.1160/th03-02-0069] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Emerging evidence supports a role for platelets in the progression of atherosclerosis in addition to an involvement in thrombotic vascular occlusion. Platelet Factor 4 (PF4), a chemokine released by activated platelets, stimulates several pro-atherogenic processes. Therefore, we examined the localization of PF4 and the homologous protein, Neutrophil Activating Protein-2 (NAP-2) in lesions representing the evolution of human atherosclerotic plaques. Carotid plaques from 132 patients with critical carotid stenosis and 6 autopsy specimens were studied. Clinical, histologic and immunohistochemical data were analyzed using a chi(2)-test. PF4 was detected in the cytoplasm of luminal and neovascular endothelium, in macrophages and in regions of plaque calcification. The presence of PF4 in macrophages and neovascular endothelium correlated with lesion grade (p = 0.004; p = 0.044). Staining of macrophages for PF4 correlated with the presence of symptomatic atherosclerotic disease (p = 0.028). In early lesions, PF4 was commonly found in macrophages of early lesions (Grade I/II), whereas NAP-2 was rarely present. In conclusion, correlation between PF4 deposition, lesion severity and symptomatic atherosclerosis suggests that persistent platelet activation may contribute to the evolution of atherosclerotic vascular lesions. These studies support the rationale for the chronic use of anti-platelet therapy in patients at risk for developing symptomatic atherosclerosis.
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Rauova L, Poncz M, McKenzie SE, Reilly MP, Arepally G, Weisel JW, Nagaswami C, Cines DB, Sachais BS. Ultralarge complexes of PF4 and heparin are central to the pathogenesis of heparin-induced thrombocytopenia. Blood 2004; 105:131-8. [PMID: 15304392 DOI: 10.1182/blood-2004-04-1544] [Citation(s) in RCA: 198] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Heparin-induced thrombocytopenia and thrombosis (HITT) is a severe complication of heparin therapy caused by antibodies to complexes between unfractionated heparin (UFH) and platelet factor 4 (PF4) that form over a narrow molar range of reactants and initiate antibody-induced platelet activation. We observed that UFH and tetrameric PF4 formed ultralarge (> 670 kDa) complexes (ULCs) only over a narrow molar range with an optimal ratio of PF4 to heparin of approximately 1:1. These ULCs were stable and visible by electron microscopy, but they could be dissociated into smaller complexes upon addition of heparin. ULCs formed inefficiently when PF4 was incubated with low-molecular-weight heparin, and none formed with the pentasaccharide fondaparinux sodium. In addition, mutation studies showed that formation of ULCs depended on the presence of PF4 tetramers. The ULCs were more reactive as determined by their capacity to bind to a HITT-like monoclonal antibody and showed greater capacity to promote platelet activation in an antibody- and FcgammaRIIA-dependent manner than were the smaller complexes. The capacity of PF4 to form ULCs composed of multiple PF4 tetramers arrayed in a lattice with several molecules of UFH may play a fundamental role in autoantibody formation, antibody-dependent platelet activation, and the propensity for thrombosis in patients with HITT.
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Sachais BS, Higazi AAR, Cines DB, Poncz M, Kowalska MA. Interactions of Platelet Factor 4 with the Vessel Wall. Semin Thromb Hemost 2004; 30:351-8. [PMID: 15282658 DOI: 10.1055/s-2004-831048] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Platelet factor 4 (PF4) is a platelet-specific protein that is stored in platelet alpha granules and released following platelet activation. PF4 was the first chemokine that was isolated, but unlike other chemokines, it may not have a clear role in inflammation. Gathering evidence suggests that unlike other chemokines that bind to specific receptors, PF4's biology depends on its unusually high affinity for heparan sulfates and other negatively charged molecules at concentrations attained in the immediate vicinity of activated platelets. There has been one report that PF4 binds to CXCR3B, a chemokine receptor isoform that may be present in some vascular beds, but the biological relevance of this single observation is not clear. We propose that the main biological role of PF4 and the basis for its presence in the alpha granules of all known mammalian platelets is to neutralize surface heparan sulfate side-chains of glycosaminoglycans and to optimize thrombus development at sites of vascular injury. In addition, the binding of PF4 to surface glycosaminoglycans may also underlie its angiostatic and proatherogenic properties. Additionally, PF4 binds to several other proteins that are central to thrombosis, angiogenesis, and atherogenesis. These interactions may also contribute to its biological and pathobiological effects. Certainly, future studies using in vivo models to test biological relevance of each of these proposed mechanisms by which PF4 interacts with the vasculature are needed, as are studies to define the importance of PF4 binding to CXCR3B.
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Yarovoi HV, Kufrin D, Eslin DE, Thornton MA, Haberichter SL, Shi Q, Zhu H, Camire R, Fakharzadeh SS, Kowalska MA, Wilcox DA, Sachais BS, Montgomery RR, Poncz M. Factor VIII ectopically expressed in platelets: efficacy in hemophilia A treatment. Blood 2003; 102:4006-13. [PMID: 12881300 DOI: 10.1182/blood-2003-05-1519] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Activated platelets release their granule content in a concentrated fashion at sites of injury. We examined whether ectopically expressed factor VIII in developing megakaryocytes would be stored in alpha-granules and whether its release from circulating platelets would effectively ameliorate bleeding in a factor VIIInull mice model. Using the proximal glycoprotein 1b alpha promoter to drive expression of a human factor VIII cDNA construct, transgenic lines were established. One line had detectable human factor VIII that colocalizes with von Willebrand factor in platelets. These animals had platelet factor VIII levels equivalent to 3% to 9% plasma levels, although there was no concurrent plasma human factor VIII detectable. When crossed onto a factor VIIInull background, whole blood clotting time was partially corrected, equivalent to a 3% correction level. In a cuticular bleeding time study, these animals also had only a partial correction, but in an FeCl3 carotid artery, thrombosis assay correction was equivalent to a 50% to 100% level. These studies show that factor VIII can be expressed and stored in platelet alpha-granules. Our studies also suggest that platelet-released factor VIII is at least as potent as an equivalent plasma level and perhaps even more potent in an arterial thrombosis model.
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