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COVID-19 convalescent plasma (CCP) with high neutralizing antibodies has been suggested in preventing disease progression in COVID-19. In this study, we investigated the relationship between clinical donor characteristics and neutralizing anti-SARS-CoV-2 antibodies in CCP donors. COVID-19 convalescent plasma donors were included into the study. Clinical parameters were recorded and anti-SARS-CoV-2 antibody levels (Spike Trimer, Receptor Binding Domain (RBD), S1, S2 and nucleocapsid protein) as well as ACE2 binding inhibition were measured. An ACE2 binding inhibition < 20% was defined as an inadequate neutralization capacity. Univariate and multivariable logistic regression analysis was used to detect the predictors of inadequate neutralization capacity. Ninety-one CCP donors (56 female; 61%) were analyzed. A robust correlation between all SARS-CoV-2 IgG antibodies and ACE2 binding inhibition, as well as a positive correlation between donor age, body mass index, and a negative correlation between time since symptom onset and antibody levels were found. We identified time since symptom onset, normal body mass index (BMI), and the absence of high fever as independent predictors of inadequate neutralization capacity. Gender, duration of symptoms, and number of symptoms were not associated with SARS-CoV-2 IgG antibody levels or neutralization. Neutralizing capacity was correlated with SARS-CoV-2 IgG antibodies and associated with time since symptom onset, BMI, and fever. These clinical parameters can be easily incorporated into the preselection of CCP donors. [ABSTRACT FROM AUTHOR]

As global vaccination campaigns against SARS-CoV-2 proceed, there is particular interest in the longevity of immune protection, especially with regard to increasingly infectious virus variants. Neutralizing antibodies (Nabs) targeting the receptor binding domain (RBD) of SARS-CoV-2 are promising correlates of protective immunity and have been successfully used for prevention and therapy. As SARS-CoV-2 variants of concern (VOCs) are known to affect binding to the ACE2 receptor and by extension neutralizing activity, we developed a bead-based multiplex ACE2-RBD inhibition assay (RBDCoV-ACE2) as a highly scalable, time-, cost-, and material-saving alternative to infectious live-virus neutralization tests. By mimicking the interaction between ACE2 and the RBD, this serological multiplex assay allows the simultaneous analysis of ACE2 binding inhibition to the RBDs of all SARS-CoV-2 VOCs and variants of interest (VOIs) in a single well. Following validation against a classical virus neutralization test and comparison of performance against a commercially available assay, we analyzed 266 serum samples from 168 COVID-19 patients of varying severity. ACE2 binding inhibition was reduced for ten out of eleven variants examined compared to wild-type, especially for those displaying the E484K mutation such as VOCs beta and gamma. ACE2 binding inhibition, while highly individualistic, positively correlated with IgG levels. ACE2 binding inhibition also correlated with disease severity up to WHO grade 7, after which it reduced. [ABSTRACT FROM AUTHOR]

The article presents Correlation between Anti-PF4 and Anti-SARS-CoV-2 Antibodies after ChAdOxl nCoV-19 Vaccination. Topics discussed include Vaccine-induced immune thrombotic thrombocytopenia (VITT), also known as thrombosis with thrombocytopenia syndrome, is a rare but potentially fatal complication of vector-based severe acute respiratory syndrome coronavirus 2 vaccines; and the clinical picture and the serologic findings in patients with VITI resemble heparin-induced thrombocytopenia.

Abstract: Background: IgG-specific anti-PF4/heparin enzyme-immunoassays (EIAs) are sensitive but not specific for platelet-activating antibodies, the cause of heparin-induced thrombocytopenia (HIT). Two features of EIA reactivity predict for presence of HIT antibodies - the magnitude of a positive result (in optical density [OD] units) and the inhibition of reactivity at high heparin concentrations - but their combined utility remains uncertain. Objective: To determine for an IgG-specific EIA how the OD values of a positive reaction and its inhibition by high heparin can be optimally combined. Methods: We screened 1,000 consecutive patients with suspected HIT using an IgG-specific PF4/heparin in-house EIA with and without high heparin (100IU/mL); and by the heparin-induced platelet activation test. Results: Platelet-activating antibodies were rarely detected (<0.2%) when the IgG-specific EIA was negative at the conventional cut-off (OD, 0.5). However, an OD cut-off of 1.0 resulted in an unacceptable loss of sensitivity (14/83=17%) for detecting platelet-activating antibodies. The high heparin step increased specificity for platelet-activating antibodies from 72% to 89% without loss of sensitivity when applied to weak-positive sera (OD≤1.0). However, decreased sensitivity was observed with strong-positive sera (OD>1.0): 11/69 such sera (16%) that did not show >40% inhibition by high heparin nevertheless contained platelet-activating antibodies. Conclusion: Specificity of an IgG-specific EIA for detecting platelet-activating antibodies can be optimized by applying the high heparin inhibition step to weak-positive reactions (0.5-≤1.0 OD). However, applying the high heparin inhibition step to strong-positive reactions (>1.0 OD) in our in-house assay risks falsely classifying a serum as negative for platelet-activating antibodies. [Copyright &y& Elsevier]

Abstract: Background: Heparin-induced thrombocytopenia (HIT) is caused by platelet-activating antibodies that recognize platelet factor 4/heparin (PF4/hep) complexes. The in vitro demonstration of PF4/hep antibodies using functional and immunological methods is essential for optimal management of patients suspected to have HIT. Since functional assays are technically challenging and limited to specialized laboratories, antigen-binding assays are commonly used in routine laboratories. Study Design: Blood samples from 448 consecutive patients in whom HIT was suspected were investigated using a latex agglutination test HemosIL® HIT-Ab(PF4-H) (HemosIL-Ab), two chemiluminescence tests HemosIL AcuStar HIT-Ab(PF4-H) (HemosIL AcuStar-Ab) and AcuStar HIT-IgG(PF4-H) (HemosIL AcuStar-IgG), an in-house PF4/hep IgG enzyme immunoassay (EIA) and the heparin induced platelet aggregation (HIPA) test. Results: Antibodies against PF4/hep were detectable in 44 out of 119 samples using HemosIL-Ab among which 20 samples were also reactive in the HIPA; and in 122, 64 and 108 out of 448 sera using HemosIL AcuStar-Ab, HemosIL AcuStar-IgG and in-house PF4/hep IgG-EIA, respectively, among which 52 sera were also reactive in the HIPA. All assays had high sensitivities of >95% for platelet activating antibodies; however, they differed in their specificities. The highest specificity and positive predictive value was observed by HemosIL AcuStar-IgG (96% and 78%, respectively). Conclusion: Automated immunoassays are useful in the laboratory investigations of HIT and present a potential improvement toward standardization of laboratory investigations of HIT. The high positive predictive capability may justify treating the patient with alternative anticoagulants without waiting for the results of a functional assay. [Copyright &y& Elsevier]