{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"bioRxiv"}],"indexed":{"date-parts":[[2026,9,5]],"date-time":"2026-09-05T10:30:03Z","timestamp":1788604203171,"version":"build-2803163510"},"posted":{"date-parts":[[2025,11,9]]},"group-title":"Cell Biology","reference-count":52,"publisher":"openRxiv","license":[{"start":{"date-parts":[[2025,11,9]],"date-time":"2025-11-09T00:00:00Z","timestamp":1762646400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"funder":[{"name":"NIH | National Heart, Lung, and Blood Institute","award":["R35HL150698"],"award-info":[{"award-number":["R35HL150698"]}]},{"name":"NIH | National Heart, Lung, and Blood Institute","award":["R01HL151730"],"award-info":[{"award-number":["R01HL151730"]}]},{"name":"NIH | National Heart, Lung, and Blood Institute","award":["R00HL177830"],"award-info":[{"award-number":["R00HL177830"]}]},{"DOI":"10.13039\/100001422","name":"American Society of Hematology","doi-asserted-by":"crossref","award":["GRT-40089313"],"award-info":[{"award-number":["GRT-40089313"]}],"id":[{"id":"10.13039\/100001422","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/100005881","name":"Hemostasis and Thrombosis Research Society","doi-asserted-by":"crossref","award":["GRT-00005101"],"award-info":[{"award-number":["GRT-00005101"]}],"id":[{"id":"10.13039\/100005881","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2025,11,9]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                <jats:p>\n                  Antiphospholipid syndrome (APS) is an immunothrombotic disorder, frequently attributed to autoantibodies that bind \u03b22-glycoprotein I (\u03b22GPI). A study showed that the platelet-specific chemokine, platelet factor 4 (PF4), binds to \u03b22GPI, enhancing recognition of \u03b22GPI by APS antibodies. APS antibodies induce the release of neutrophil extracellular traps (NETs), webs of decondensed chromatin that bind both PF4 and \u03b22GPI. We propose that PF4 bridges \u03b22GPI to NETs (and other PF4-targeted polyanions), leading to the formation of prothrombotic PF4:\u03b22GPI:NET immunotargets in APS. Dynamic light-scattering studies of isolated IgGs from four patients with triple-positive APS show formation of PF4:\u03b22GPI:NET complexes that bind APS antibodies. NETs released in a microfluidic system bound \u03b22GPI, but only in the presence of PF4, forming a multimolecular APS antigenic target. Whole blood infused through a photochemically-injured, endothelium-lined microfluidic channel formed platelet-, fibrin-, and complement-rich thrombi that bound APS antibody only in the presence of PF4. Thrombi were reduced in size if either ADAMTS13 or DNase1 was infused. In a murine APS model, wildtype and transgenic mice expressing platelet human PF4 \u00b1 Fc\u03b3RIIA developed more intense neutrophil rolling along veins, and more extensive thrombus formation following laser injury to cremaster arterioles and venules, whereas mice lacking PF4 did not. Three antigenically distinct anti-hPF4 monoclonal antibodies blocked thrombosis\n                  <jats:italic>in vitro<\/jats:italic>\n                  , and neutrophil rolling and thrombosis\n                  <jats:italic>in vivo<\/jats:italic>\n                  . Our studies provide new insights into the basis of APS that has mechanistic parallels to other known PF4 immunothrombotic disorders and offer potential diagnostic and non-anticoagulant therapeutic strategies for clinical management.\n                <\/jats:p>\n                <jats:sec id=\"s1\">\n                  <jats:title>Key points<\/jats:title>\n                  <jats:list list-type=\"bullet\">\n                    <jats:list-item>\n                      <jats:p>PF4 enhances \u03b22GPI binding to NETs and these complexes are central to APS immunothrombosis.<\/jats:p>\n                    <\/jats:list-item>\n                    <jats:list-item>\n                      <jats:p>Anti-PF4 monoclonal antibodies block APS immunothrombosis in microfluidic and murine studies.<\/jats:p>\n                    <\/jats:list-item>\n                  <\/jats:list>\n                <\/jats:sec>","DOI":"10.1101\/2025.11.07.687095","type":"posted-content","created":{"date-parts":[[2025,11,11]],"date-time":"2025-11-11T19:19:12Z","timestamp":1762888752000},"source":"Crossref","is-referenced-by-count":2,"title":["Antiphospholipid syndrome (APS) is a platelet factor 4 (PF4)-centric immunothrombotic disorder"],"prefix":"10.64898","author":[{"given":"Conroy O.","family":"Field","sequence":"first","affiliation":[{"name":"Pharmacology Graduate Group, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA"},{"name":"Division of Hematology, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Amrita","family":"Sarkar","sequence":"additional","affiliation":[{"name":"Division of Hematology, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"},{"name":"Department of Pediatrics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Khalil","family":"Bdeir","sequence":"additional","affiliation":[{"name":"Department of Pathology and Laboratory Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hyunjun","family":"Kim","sequence":"additional","affiliation":[{"name":"Division of Hematology, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Santosh K.","family":"Yadav","sequence":"additional","affiliation":[{"name":"Division of Hematology, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jenna","family":"Oberg","sequence":"additional","affiliation":[{"name":"Division of Hematology, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Guohua","family":"Zhou","sequence":"additional","affiliation":[{"name":"Division of Hematology, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Steven","family":"Jiang","sequence":"additional","affiliation":[{"name":"Division of Hematology, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Manas","family":"Gumedelli","sequence":"additional","affiliation":[{"name":"Division of Hematology, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Keith R.","family":"McCrae","sequence":"additional","affiliation":[{"name":"Taussig Cancer Institute and Department of Cardiovascular and Metabolic Sciences, Cleveland Clinic Lerner College of Medicine, Cleveland, OH"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gowthami M.","family":"Arepally","sequence":"additional","affiliation":[{"name":"Division of Hematology, Duke University School of Medicine, Durham, NC"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jerome","family":"Rollin","sequence":"additional","affiliation":[{"name":"Department of Hemostasis, University Hospital Center of Tours, and INSERM UMR1327, University of Tours, Tours, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yves","family":"Gruel","sequence":"additional","affiliation":[{"name":"Department of Hemostasis, University Hospital Center of Tours, and INSERM UMR1327, University of Tours, Tours, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Thomas L.","family":"Ortel","sequence":"additional","affiliation":[{"name":"Division of Hematology, Duke University School of Medicine, Durham, NC"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"M. 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