TY - JOUR T1 - Production of anti-PF4 antibodies in antiphospholipid antibody-positive patients is not affected by COVID-19 vaccination JF - RMD Open JO - RMD Open DO - 10.1136/rmdopen-2021-001902 VL - 8 IS - 1 SP - e001902 AU - Paola Adele Lonati AU - Caterina Bodio AU - Mariangela Scavone AU - Giuliana Martini AU - Elisa Pesce AU - Alessandra Bandera AU - Andrea Lombardi AU - Maria Gerosa AU - Franco Franceschini AU - Angela Tincani AU - Gianmarco Podda AU - Sergio Abrignani AU - Renata Grifantini AU - Marco Cattaneo AU - Maria Orietta Borghi AU - Pier Luigi Meroni Y1 - 2022/02/01 UR - http://rmdopen.bmj.com/content/8/1/e001902.abstract N2 - 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. ER -