Analytical and clinical evaluation of four commercial SARS-CoV-2 serological immunoassays in hospitalized patients and ambulatory individuals.

BACKGROUND: This study aimed to compare four anti-SARS-CoV-2 immunoassays in populations presenting different clinical severity levels. METHODS: Three populations were included: "severe-to-critical" ICU-hospitalized patients (n = 18), "mild-to-moderate" hospitalized patients (n = 16) and non-hospitalized symptomatic patients (n = 24). Four commercial immunoassays were analyzed and validated: anti-IgG ARCHITECT® (Abbott), anti-Total antibodies (Ab) VITROS® (Ortho Clinical Diagnostics), anti-IgG NovaLisa® (NovaTec Immundiagnostica) and Healgen® IgM and IgG (Zhejiang Orient Gene Biotech). Sensitivities were evaluated according to days post-symptoms onset (pso). Specificities were evaluated on SARS-CoV-2-negative control sera collected before January 2020. RESULTS: A majority of severe-to-critically ill patients showed detectable Ab already at day 14 and sensitivities reached 100 % after 22 days pso. For patients with "mild-to-moderate" illness, sensitivities increased by at least 5-fold from day 0 to day 14 pso. Non-hospitalized symptomatic individuals already seroconverted at day 14 days pso with 100 % sensitivities for Total Ab VITROS®. Specificities were evaluated at 97 % for ARCHITECT® and NovaLisa®, 98 % for VITROS® and at 94 % for Healgen® combined IgM and IgG. Five "severe-to-critically" ill patients presented high positive Ab levels for at least 16 weeks pso. CONCLUSION: The Ab levels and the evaluated sensitivities, representing the true positive rate, increased overtime and were related to the COVID-19 severity. Automated Total Ab immunoassay showed better sensitivities and specificity for immunological surveillance and vaccine evaluation.

[Role of erythrocyte deformability in erythrocyte transit time and bioavailability of O2]. / Role de la déformabilité érythrocytaire sur le temps de transit globulaire et la biodisponibilité de l'O2.

The bioavailability of oxygen and its transfer towards all of the cells of the body essentially depends on the flow rate of red blood cells in the capillaries, which often have a smaller diameter than the red cell itself. The authors discuss the results obtained for the mean transit time of erythrocytes, based on microfiltration through artificial polycarbonate capillaries with a diameter of 5 microns, a length of 13 microns and a density of 4.10(5) pores/cm2.

[Blood microfiltration methods]. / Les méthodes de microfiltration sanguine.

Red cell deformability can be approached by filtration through narrow channels either at constant pressure or at constant flow. A very simplified constant pressure method is described, measuring relative flow of 8% hematocrit red cells resuspended in buffer. A constant flow method is also described, using again 8 to 10% hematocrit, which the authors consider as more physiological than the very low hematocrits used by others. Significant results are obtained after incubation with pentoxifylline.

Assessment of erythrocyte deformability by constant flow filtration technique: analysis of factors influencing the initial pressure.

When filtering red blood cells (RBC) resuspended into buffer at constant flow, the pressure-time curve is dependent on erythrocyte deformability (E.D) and also on the plugging of pores by RBC or leukocytes (WBC). To understand the influence of these 3 factors, we used an apparatus with: 1) a constant flow syringe (Bioblock) (1.56 ml/mn); 2) a pressure transducer (Statham P23 ID); 3) a recorder (Gould); 4) a 5 micron polycarbonate filter (Nuclepore) housed in a lucite block according to USAMI & al. (1). Resuspensions of RBC from 4 to 14% haematocrit with 0 to 600 WBC/mm3 were investigated. Results indicate that: 1/ The first inflexion point of the pressure-time curve (initial pressure leading to calculation of beta) is related to the RBC's deformability; 2/beta is (in our experimental conditions) dependent on the WBC number; 3/beta seems very sensitive to deformability changes as shown by rapid increases induced by osmolarity changes.

From Virchow to red cells (the unended quest).

For Virchow vessel wall, coagulability and flow were the three eventual culprits of thrombogenesis. Pharmacological progress in the three fields has not been parallel. Strangely enough they have found possible therapy in the order of their description: first the vessel wall with vasodilators. Then 'coagulability' with anticoagulants, thrombolytics, antiaggregants. It is only more recently that new methods of investigation have allowed assessment and pharmacology of the main determinant of flow in microvessels: red cell deformability.