Production of anti-PF4 antibodies in antiphospholipid antibody-positive patients is not affected by COVID-19 vaccination

Paola Adele Lonati, Caterina Bodio, Mariangela Scavone, Giuliana Martini, Elisa Pesce, Alessandra Bandera, Andrea Lombardi, Maria Gerosa, Franco Franceschini, Angela Tincani, Gianmarco Podda, Sergio Abrignani, Renata Grifantini, Marco Cattaneo, Maria Orietta Borghi, Pier Luigi Meroni

Research output: Contribution to journalArticlepeer-review


Background Antibodies against cationic platelet chemokine, platelet factor 4 (PF4/CXCL4), have been described in heparin-induced thrombocytopenia (HIT), but also in patients positive for antiphospholipid antibodies (aPL) even in the absence of heparin treatment and HIT-related clinical manifestations. Anti-PF4 antibodies have been recently described also in subjects who developed thrombosis with thrombocytopenia syndrome (TTS) in association with adenoviral vector-based, but not with mRNA-based, COVID-19 vaccines. Objective To investigate whether COVID-19 vaccination affects the production of anti-PF4 antibodies in aPL-positive patients and in control groups. Methods Anti-PF4 immunoglobulins were detected in patients' and controls' serum samples by ELISA and their ability to activate normal platelets was assessed by the platelet aggregation test. Results Anti-PF4 were found in 9 of 126 aPL-positive patients, 4 of 50 patients with COVID-19, 9 of 49 with other infections, and 1 of 50 aPL-negative patients with systemic lupus erythematosus. Clinical manifestations of TTS were not observed in any aPL patient positive for anti-PF4, whose serum failed to cause platelet aggregation. The administration of COVID-19 vaccines did not affect the production of anti-PF4 immunoglobulins or their ability to cause platelet aggregation in 44 aPL-positive patients tested before and after vaccination. Conclusions Heparin treatment-independent anti-PF4 antibodies can be found in aPL-positive patients and asymptomatic carriers, but their presence, titre as well as in vitro effect on platelet activation are not affected by COVID-19 vaccination.

Original languageEnglish
Article numbere001902
JournalRMD Open
Issue number1
Publication statusPublished - Feb 7 2022


  • antibodies
  • antiphospholipid
  • COVID-19
  • vaccination

ASJC Scopus subject areas

  • Immunology and Allergy
  • Rheumatology
  • Immunology


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