{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"bioRxiv"}],"indexed":{"date-parts":[[2026,7,20]],"date-time":"2026-07-20T19:03:40Z","timestamp":1784574220776,"version":"3.55.0"},"posted":{"date-parts":[[2026,7,17]]},"group-title":"Microbiology","reference-count":76,"publisher":"openRxiv","license":[{"start":{"date-parts":[[2026,7,17]],"date-time":"2026-07-17T00:00:00Z","timestamp":1784246400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100000050","name":"National Heart Lung and Blood Institute","doi-asserted-by":"crossref","award":["63199"],"award-info":[{"award-number":["63199"]}],"id":[{"id":"10.13039\/100000050","id-type":"DOI","asserted-by":"crossref"}]},{"name":"Flinn Foundation","award":["23-12140"],"award-info":[{"award-number":["23-12140"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2026,7,16]]},"abstract":"<jats:title>ABSTRACT<\/jats:title>\n                <jats:p>\n                  Platelet Factor 4 (PF4), a cationic antimicrobial peptide, serves as a ligand for the myeloid-specific phagocytic receptor CR3 (Mac-1, CD11b\/CD18). We previously demonstrated that recombinant dimeric PF4 (rdPF4) functions as a bacterial opsonin, enhancing phagocytosis of Gram-positive\n                  <jats:italic>Staphylococcus aureus<\/jats:italic>\n                  and facilitating clearance of both antibiotic-susceptible and methicillin-resistant\n                  <jats:italic>S. aureus<\/jats:italic>\n                  in a mouse model of infectious peritonitis. In this study, we examined whether rdPF4 is pathogen-agnostic by assessing its effect on phagocytosis of Gram-negative encapsulated\n                  <jats:italic>Klebsiella pneumoniae<\/jats:italic>\n                  , a WHO Bacterial Priority Pathogen. We demonstrate that rdPF4 enhances CR3-mediated phagocytosis of both live and heat-inactivated high-virulence K2 and low-virulence K3 strains of\n                  <jats:italic>K. pneumoniae<\/jats:italic>\n                  by various mouse and human macrophage cell lines, as well as primary neutrophils and macrophages. It also increased phagocytosis of carbapenem-resistant\n                  <jats:italic>K. pneumoniae<\/jats:italic>\n                  . rdPF4 did not directly kill bacteria but acted as an opsonin binding to the negatively charged bacterial capsule and creating recognition sites for CR3 on leukocytes. In a mouse sepsis model, a single dose of rdPF4 significantly enhanced bacterial clearance from the lungs, liver, and peritoneum and reduced bacteremia. Histological analyses showed that rdPF4 provided substantial protection to lung and liver tissues against\n                  <jats:italic>K. pneumoniae<\/jats:italic>\n                  -induced damage. Consistent with these findings, rdPF4 treatment increased the survival rates of infected mice. These results show that rdPF4 effectively targets the capsule, a key virulence factor of\n                  <jats:italic>K. pneumoniae<\/jats:italic>\n                  , thereby reducing the bacterium\u2019s ability to evade the host immune response. Overall, the data suggest a common mechanism in which cationic rdPF4, by binding to the negatively charged surfaces of both Gram-negative and Gram-positive bacteria, diminishes their antiphagocytic properties.\n                <\/jats:p>","DOI":"10.64898\/2026.07.14.737852","type":"posted-content","created":{"date-parts":[[2026,7,17]],"date-time":"2026-07-17T16:35:13Z","timestamp":1784306113000},"source":"Crossref","is-referenced-by-count":0,"title":["TARGETING THE CAPSULE OF\n                  <i>KLEBSIELLA PNEUMONIAE<\/i>\n                  WITH A CATIONIC CR3-BINDING PROTEIN ENHANCES PHAGOCYTOSIS AND PROMOTES BACTERIAL CLEARANCE AND SURVIVAL IN A MOUSE SEPSIS MODEL"],"prefix":"10.64898","author":[{"given":"Nataly P.","family":"Podolnikova","sequence":"first","affiliation":[{"name":"From the School of Life Sciences, Arizona State University, Tempe, AZ 85287, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Iryna","family":"Klymenko","sequence":"additional","affiliation":[{"name":"From the School of Life Sciences, Arizona State University, Tempe, AZ 85287, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"James","family":"Alagna","sequence":"additional","affiliation":[{"name":"From the School of Life Sciences, Arizona State University, Tempe, AZ 85287, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Cyrus","family":"Diercksmeier","sequence":"additional","affiliation":[{"name":"From the School of Life Sciences, Arizona State University, Tempe, AZ 85287, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Arnat","family":"Balabiyev","sequence":"additional","affiliation":[{"name":"From the School of Life Sciences, Arizona State University, Tempe, AZ 85287, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"David","family":"Richardson","sequence":"additional","affiliation":[{"name":"bioSyntagma Inc., Tempe, AZ 85282, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4449-5140","authenticated-orcid":false,"given":"Tatiana P.","family":"Ugarova","sequence":"additional","affiliation":[{"name":"From the School of Life Sciences, Arizona State University, Tempe, AZ 85287, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"54368","reference":[{"key":"2026072011350939000_2026.07.14.737852v1.1","doi-asserted-by":"publisher","DOI":"10.1128\/MMBR.00078-15"},{"issue":"2","key":"2026072011350939000_2026.07.14.737852v1.2","doi-asserted-by":"crossref","first-page":"123","DOI":"10.1093\/femsre\/fuy043","article-title":"Klebsiella pneumoniae infection biology: living to counteract host defences","volume":"43","year":"2019","journal-title":"FEMS Microbiol Rev"},{"key":"2026072011350939000_2026.07.14.737852v1.3","doi-asserted-by":"crossref","unstructured":"Gonzalez-Ferrer S , Pe\u00f1aloza HF , Budnick JA , Bain WG , Nordstrom HR , Lee JS , et al. 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