A novel competition ELISA for the rapid quantification of SARS-CoV-2 neutralizing antibodies in convalescent plasma.

BACKGROUND: COVID-19 convalescent plasma (CCP) ideally contains high titers of (neutralizing) anti-SARS-CoV-2 antibodies. Several scalable immunoassays for CCP selection have been developed. We designed an enzyme-linked immunosorbent assay (ELISA) that measures neutralizing antibodies (of all isotypes) in plasma by determining the level of competition between CCP and a mouse neutralizing antibody for binding to the receptor binding domain (RBD) of SARS-CoV-2. METHODS: Plasma was collected from 72 convalescent individuals and inhibition of viral infection was determined by plaque reduction neutralization (PRNT50). The level of neutralizing antibodies was measured in the novel competition ELISA and in a commercially available ELISA that measures inhibition of recombinant ACE2 binding to immobilized RBD. These results were compared with a high throughput chemiluminescent microparticle immunoassay (CMIA). RESULTS: The results from both ELISAs were correlating, in particular for high titer CCP (PRNT50 ≥ 1:160) (Spearman r = .73, p < .001). Moderate correlation was found between the competition ELISA and CMIA (r = .57 for high titer and r = .62 for low titer CCP, p < .001). Receiver operator characteristic analysis showed that the competition ELISA selected CCP with a sensitivity and specificity of 61% and 100%, respectively. However, discrimination between low and high titer CCP had a lower resolution (sensitivity: 34% and specificity: 89%). CONCLUSION: The competition ELISA screens for neutralizing antibodies in CCP by competition for just a single epitope. It exerts a sensitivity of 61% with no false identifications. These ELISA designs can be used for epitope mapping or for selection of CCP.

Hemoglobin screening in blood donors: a prospective study assessing the value of an invasive and a noninvasive point-of-care device for donor safety.

BACKGROUND: Low hemoglobin (Hb) levels are a common reason for whole blood donor deferral. As some of the deferred donors do not return to donate blood later, the development of accurate tools to reliably detect low Hb levels is therefore important for donor safety and retention. STUDY DESIGN AND METHODS: In a prospective study, 1483 whole blood donors were enrolled in three study arms. In each study arm the Hb results measured with a point-of-care testing device were compared with the venous Hb results obtained in our central laboratory. Both an invasive capillary Hb (Compolab) and a noninvasive spectroscopy Hb (Haemospect) were tested. For the latter, two different application methods for the positioning of the Digiclip were assessed. In a second phase the Compolab was tested in routine conditions. RESULTS: The Haemospect device failed to reliably identify donors with Hb levels below the European cutoffs (125 g/L for females and 135 g/L for males). In contrast, the Compolab identified 72.4% of first-time donors and 78.9% of regular donors with Hb levels below these cutoffs. In routine conditions, the Compolab identified the majority of donors with low Hb levels. CONCLUSION: Differences between Hb levels measured with invasive and noninvasive point-of-care devices and measured on venous samples exist. Implementing the Compolab at collection sites provides a high level of safety toward first-time donors.

Glucocorticoid receptor DNA methylation and childhood trauma in chronic fatigue syndrome patients.

OBJECTIVE: Although the precise mechanisms are not yet understood, previous studies have suggested that chronic fatigue syndrome (CFS) is associated with hypothalamic-pituitary-adrenal (HPA) axis dysregulation and trauma in early childhood. Consistent with findings suggesting that early life stress-induced DNA methylation changes may underlie dysregulation of the HPA axis, we previously found evidence for the involvement of glucocorticoid receptor (GR) gene (NR3C1) methylation in whole blood of CFS patients. METHODS: In the current study, we assessed NR3C1-1F region DNA methylation status in peripheral blood from a new and independent sample of 80 female CFS patients and 91 female controls. In CFS patients, history of childhood trauma subtypes was evaluated using the Childhood Trauma Questionnaire short form (CTQ-SF). RESULTS: Although absolute methylation differences were small, the present study confirms our previous findings of NR3C1-1F DNA hypomethylation at several CpG sites in CFS patients as compared to controls. Following multiple testing correction, only CpG_8 remained significant (DNA methylation difference: 1.3% versus 1.5%, p<0.001). In addition, we found associations between DNA methylation and severity of fatigue as well as with childhood emotional abuse in CFS patients, although these findings were not significant after correction for multiple testing. CONCLUSIONS: In conclusion, we replicated findings of NR3C1-1F DNA hypomethylation in CFS patients versus controls. Our results support the hypothesis of HPA axis dysregulation and enhanced GR sensitivity in CFS.