An original multiplex method to assess five different SARS-CoV-2 antibodies.

OBJECTIVES: Accurate SARS-CoV-2 serological assays are urgently needed to help diagnose infection, determine past exposure of populations and assess the response to future vaccines. The study aims at assessing the performance of the multiplex D-tek COVIDOT 5 IgG assay for the detection of SARS-CoV-2 IgG antibodies (N, S1+S2, S1, S2 and RBD). METHODS: Sensitivity and dynamic trend to seropositivity were evaluated in 218 samples obtained from 46 rRT-PCR confirmed COVID-19 patients. Non-SARS-CoV-2 sera (n=118) collected before the COVID-19 pandemic with a potential cross-reaction to the SARS-CoV-2 immunoassay were included in the specificity analysis. RESULTS: A gradual dynamic trend since symptom onset was observed for all IgG antibodies. Sensitivities before day 14 were suboptimal. At ≥21 days, sensitivities reached 100% (93.4-100%) for N, S1+S2, S2 and RBD-directed IgG and 96.3% (87.3-99.6%) for S1-directed IgG. In 42 out of 46 patients (91.3%), all five antibodies were detected at ≥14 days. The four remaining patients had between 2 and 4 positive antibodies at their respective maximal follow-up period. The specificity was 100 % for S1+S2, S2 and RBD, 98.3% for N and 92.4% (86.0-96.5%) for S1-directed IgG. The combined use of antigens increases the early sensitivity whilst enforcing high specificity. CONCLUSIONS: Sensitivities at ≥21 days and specificities were excellent, especially for N, S1+S2, S2 and RBD-directed IgG. Caution is however required when interpreting single S1-directed reactivities. Using a multiplex assay complies with the orthogonal testing algorithm of the CDC and allows a better and critical interpretation of the serological status of a patient.

Prevalence of Myositis-Specific Antibodies in Idiopathic Interstitial Pneumonias.

Although included in the serological domain of the 'interstitial pneumonia with auto-immune features' (IPAF) research statement, the search for myositis-specific antibodies (MSA) is not incorporated in routine clinical practice. The objective of the study was to evaluate MSA prevalence in an idiopathic interstitial pneumonia (IIP) cohort (n = 68) with suggestive morphological interstitial lung disease patterns. Twelve of 68 patients (17.6%) carried MSA, whereof only two were anti-nuclear antibody-positive. Besides female gender, no demographic or pulmonary function parameter was predictive for MSA positivity. MSA were present in 32.4% of IPAF patients (n = 37), being essential for IPAF diagnosis in four of them (10.8%).

Screening for lipoprotein receptor-related protein 4-, agrin-, and titin-antibodies and exploring the autoimmune spectrum in myasthenia gravis.

In autoimmune myasthenia gravis (MG), the identification of antibodies and characterization of serological subgroups is of great importance for diagnosis and management of the disease. Our aims were to study the frequency of antibodies against lipoprotein-related protein 4 (LRP4), agrin, and titin using the most recent techniques, and to characterize corresponding clinical features and autoimmune diseases (AID) in 100 MG-patients. The antibody frequencies in the 55 AChR-antibody positive patients were 7% LRP4, 5% agrin, 53% titin, and in the 45 AChR-antibody negative patients 2% MuSK, 2% LRP4, 2% agrin, and 27% titin. LRP4-MG presented late-onset age, mild symptoms, good therapeutic response, and no thymic changes. Agrin-MG showed early onset age, mild-to-severe symptoms, and moderate treatment response. The phenotype of titin-MG depended on AChR-antibodies: AChR-antibody negative patients presented with mostly mild limb muscle weakness, whereas AChR-antibody positive patients showed more frequently severe symptoms, including myasthenic crisis, bulbar predominance, and thymoma. Additional AID were detected in 32% of MG-patients, most frequently Hashimoto's thyroiditis (21%). Based on our data, we recommend the detection of LRP4-antibodies for at least AChR-antibody negative MG-patients and titin-antibodies for all MG-patients. We propose taking an accurate medical history for typical symptoms of Hashimoto's thyroiditis in MG-patients.

Do associated auto-antibodies influence the outcome of myasthenia gravis after thymectomy?

Myasthenia gravis (MG) is a neuromuscular autoimmune disease, where antibodies against the acetylcholine receptor destroy this receptor. The role of thymectomy in the treatment of MG remains controversial. Because of the frequent association with other autoimmune diseases, we hypothesized that patients with multiple autoantibodies (autoAbs) might have a lower chance of reaching complete stable remission after thymectomy. We analyzed sera of 85 MG patients who underwent a thymectomy between April 2004 and December 2012. We used four different immunodot kits (D-Tek, Mons, Belgium): ANA25 Quantrix, Synthetase 10 Diver, Myositis 7 Diver and Liver 10 profile Diver, all automatized on the BlueDiver Instrument (D-Tek). The Myasthenia Gravis Foundation of America (MGFA) postintervention status was used to determine the outcome after thymectomy. AutoAbs other than anti-acetylcholine receptor (AChR) antibodies were detected in 29.4% of the patients of whom 16.5% clinically had a second autoimmune disease. In none of the seronegative patients other autoAbs were detected. No significant difference was observed in the 3-years remission rate after thymectomy in patients with or without antibodies other than anti-AChR antibodies. Although these autoAbs do not predict outcome in our MG patient cohort, screening for multiple autoAbs in MG patients might be warranted to identify patients with additional autoimmune diseases.