The production of anti-PF4 antibodies in anti-phospholipid antibody-positive patients is not affected by COVID-19 vaccination

Antibodies against cationic platelet chemokine, platelet factor 4 (PF4/CXCL4) have been described in heparin-induced thrombocytopenia (HIT) but also in patients positive for anti-phospholipid 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. We investigated whether COVID-19 vaccination affects the production of anti-PF4 immunoglobulins detectable by solid phase assay in aPL-positive patients and their ability to induce in vitro platelet activation. Anti-PF4 were found in 9/126 aPL-positive patients, 4/50 COVID-19, 9/49 other infections and 1/50 aPL-negative systemic lupus erythematosus patients. Clinical manifestations of TTS were not observed in any aPL patient positive for anti-PF4, whose sera failed to cause platelet aggregations. 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. In conclusion, heparin treatment-independent anti-PF4 antibodies can be found in aPL-positive patients and asymptomatic carriers, but their presence, titer as well as in vitro effect on platelet activation are not affected by COVID-19 vaccination.

Prevalence, specificity, and clinical association of anti-phospholipid antibodies in COVID-19 patients: are the antibodies really guilty?

BackgroundCritically ill patients with coronavirus disease 2019 (COVID-19) have a profound hypercoagulable state and often develop coagulopathy which leads to organ failure and death. Because of a prolonged activated partial-thromboplastin time (aPTT), a relationship with anti-phospholipid antibodies (aPL) has been proposed, but results are controversial. Functional assays for aPL (i.e., lupus anticoagulant) can be influenced by concomitant anticoagulation and/or high levels of C reactive protein. The presence of anti-cardiolipin (aCL), anti-beta2-glycoprotein I (anti-{beta}2GPI) and anti-phosphatidylserine/prothrombin (aPS/PT) antibodies was not investigated systematically. Epitope specificity of anti-{beta}2GPI antibodies was not reported. ObjectiveTo evaluate the prevalence and the clinical association of aPL in a large cohort of COVID-19 patients, and to characterize the epitope specificity of anti-{beta}2GPI antibodies. MethodsELISA and chemiluminescence assays were used to test 122 sera of patients suffering from severe COVID-19. Of them, 16 displayed major thrombotic events. ResultsAnti-{beta}2GPI IgG/IgA/IgM were the most frequent in 15.6/6.6/9.0% of patients, while aCL IgG/IgM were detected in 5.7/6.6% by ELISA. Comparable values were found by chemiluminescence. aPS/PT IgG/IgM were detectable in 2.5 and 9.8% by ELISA. No association between thrombosis and aPL was found. Reactivity against domain 1 and 4-5 of {beta}2GPI was limited to 3/58 (5.2%) tested sera for each domain and did not correlate with aCL/anti-{beta}2GPI nor with thrombosis. ConclusionsaPL show a low prevalence in COVID-19 patients and are not associated with major thrombotic events. aPL in COVID-19 patients are mainly directed against {beta}2GPI but display an epitope specificity different from antibodies in antiphospholipid syndrome.

Anti-RNA polymerase III antibodies: a marker of systemic sclerosis with rapid onset and skin thickening progression.

Anti-RNA polymerase III antibodies (ARA) are a specific marker for Systemic Sclerosis (SSc), associated to severe disease with major organ and diffuse cutaneous involvement. In our series, ARA were found in 19 of 216 sera, in 15 cases as isolated antibodies' specificity, with a statistically negative association with other SSc-specific autoantibodies (p: 0.00003). The prevalence of ARA among 73 anticentromere and anti-topoisomerase I (topo I) negative sera, was 20.5%. Patients with isolated ARA had more rapid disease onset, defined as the interval from the appearance of Raynaud's phenomenon to the first symptom other than Raynaud's, than patients with isolated anti-topo I antibodies (median: 2 months vs 13 months; p: 0.0013). A rapid onset of SSc (within 6 months from Raynaud's phenomenon onset) was found in all patients with isolated ARA and only in 34% of those with anti-topo I (p<0.00001). Moreover, the skin thickening in the first months after SSc onset was faster in the ARA group (p<0.0001). Nevertheless, the rates of internal organ involvement and of survival rates were similar between the two groups. Our experience therefore suggests that ARA are a marker of very rapid onset of disease and skin thickening progression in SSc.

Complement activation in anti-phospholipid syndrome: a clue for an inflammatory process?

Anti-phospholipid syndrome (APS) is defined by recurrent arterial/venous thrombosis and/or fetal losses in the persistent presence of anti-phospholipid antibodies (aPL). In in vivo experimental models aPL thrombogenic activity is associated with a pro-inflammatory endothelial phenotype (increased adhesion molecule [ADM] expression and leukocyte adhesion) in addition to a pro-coagulant one (tissue factor [TF] expression). This is in line with the in vitro aPL ability to trigger intracellular signalling and to up-regulate ADM, TF and pro-inflammatory cytokine/chemokine expression at the mRNA and protein level in endothelial cells. Comparable effects were also reported in monocytes in vitro. In addition, complement activation is required by aPL to display their thrombogenic activity in in vivo models. Interestingly, complement activation blocking as well as Tumor Necrosis Factor alpha neutralization protect animals from aPL-induced fetal losses. Altogether these findings speak in favour for a role of inflammation in APS in spite of the absence of a clear inflammatory signature in the patients. We could not find any complement (C3c and C4d) deposition in the placentas from 2 late abortions (20 weeks of gestation) in APS women. Further studies are necessary to investigate whether complement activation and inflammatory processes found in animal models are taking place in APS patients.