Anti-PF4 immunothrombosis without proximate heparin or adenovirus vector vaccine exposure.

ABSTRACT: Platelet-activating anti-platelet factor 4 (PF4)/heparin antibodies and anti-PF4 antibodies cause heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombocytopenia and thrombosis (VITT), respectively. Diagnostic and treatment considerations differ somewhat between HIT and VITT. We identified patients with thrombocytopenia and thrombosis without proximate heparin exposure or adenovirus-based vaccination who tested strongly positive by PF4/polyanion enzyme-immunoassays and negative/weakly positive by heparin-induced platelet activation (HIPA) test but strongly positive by PF4-induced platelet activation (PIPA) test (ie, VITT-like profile). We tested these patients by a standard chemiluminescence assay that detects anti-PF4/heparin antibodies found in HIT (HemosIL AcuStar HIT-IgG(PF4-H)) as well as a novel chemiluminescence assay for anti-PF4 antibodies found in VITT. Representative control sera included an exploratory anti-PF4 antibody-positive but HIPA-negative/weak cohort obtained before 2020 (n = 188). We identified 9 patients with a clinical-pathological profile of a VITT-like disorder in the absence of proximate heparin or vaccination, with a high frequency of stroke (arterial, n = 3; cerebral venous sinus thrombosis, n = 4), thrombocytopenia (median platelet count nadir, 49 × 109/L), and hypercoagulability (greatly elevated D-dimer levels). VITT-like serological features included strong reactivity by PIPA (aggregation <10 minutes in 9/9 sera) and positive testing in the novel anti-PF4 chemiluminescence assay (3/9 also tested positive in the anti-PF4/heparin chemiluminescence assay). Our exploratory cohort identified 13 additional patient sera obtained before 2020 with VITT-like anti-PF4 antibodies. Platelet-activating VITT-like anti-PF4 antibodies should be considered in patients with thrombocytopenia, thrombosis, and very high D-dimer levels, even without a proximate exposure to heparin or adenovirus vector vaccines.

Diagnostic utility of anti-Ro52 detection in systemic autoimmunity.

OBJECTIVES: To determine the prevalence and diagnostic utility of monospecific anti-Ro52 (defined as an immune response against Ro-52 antigen in the absence of reactivity to Ro-60 antigen) reactivity in selected autoimmune diseases. STUDY DESIGN: Stored diagnostic non-consecutive serum samples obtained from patients with systemic lupus erythematosus (SLE), primary Sjögren's syndrome (pSS), systemic sclerosis, idiopathic inflammatory myopathies (IIM), rheumatoid arthritis, primary biliary cirrhosis and mixed essential cryoglobulinaemia were analysed by line immunoassay to detect the presence of anti-Ro52 and other autoantibodies. RESULTS: Monospecific anti-Ro52 reactivity was found in 51 (12.7%) of the 402 samples tested. Anti-Ro52 was the most common serological marker in patients with IIM (35/147, 23.8%) and co-occurred with anti-Jo1 (10/18, 55.6%; p=0.02). The prevalence of anti-Ro52 reactivity was significantly more than anti-Ro60 reactivity in patients with IIM, systemic sclerosis, primary biliary cirrhosis, mixed essential cryoglobulinemia and pSS. The mean signal intensity of anti-Ro52 reactivity was significantly higher in pSS than SLE and associated with rheumatoid factor positivity. The mean signal intensity of anti-Ro52 correlated with anti-Ro60 and anti-La in pSS and SLE. CONCLUSIONS: Monospecific anti-Ro52 reactivity is not disease specific but may be of importance in patients with IIM. Furthermore, as anti-Ro52 reactivity is more prevalent than anti-Ro60 reactivity in certain autoimmune conditions, specific testing for their distinction in clinical practice is recommended.