RBD-Based ELISA and Luminex Predict Anti-SARS-CoV-2 Surrogate-Neutralizing Activity in Two Longitudinal Cohorts of German and Spanish Health Care Workers.

The ability of antibodies to neutralize severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an important correlate of protection. For routine evaluation of protection, however, a simple and cost-efficient anti-SARS-CoV-2 serological assay predictive of serum neutralizing activity is needed. We analyzed clinical epidemiological data and blood samples from two cohorts of health care workers in Barcelona and Munich to compare several immunological readouts for evaluating antibody levels that could be surrogates of neutralizing activity. We measured IgG levels against SARS-CoV-2 spike protein (S), its S2 subunit, the S1 receptor binding domain (RBD), and the full length and C terminus of nucleocapsid (N) protein by Luminex, and against RBD by enzyme-linked immunosorbent assay (ELISA), and assessed those as predictors of plasma surrogate-neutralizing activity measured by a flow cytometry assay. In addition, we determined the clinical and demographic factors affecting plasma surrogate-neutralizing capacity. Both cohorts showed a high positive correlation between IgG levels to S antigen, especially to RBD, and the levels of plasma surrogate-neutralizing activity, suggesting RBD IgG as a good correlate of plasma neutralizing activity. Symptomatic infection, with symptoms such as loss of taste, dyspnea, rigors, fever and fatigue, was positively associated with anti-RBD IgG positivity by ELISA and Luminex, and with plasma surrogate-neutralizing activity. Our serological assays allow for the prediction of serum neutralization activity without the cost, hazards, time, and expertise needed for surrogate or conventional neutralization assays. Once a cutoff is established, these relatively simple high-throughput antibody assays will provide a fast and cost-effective method of assessing levels of protection from SARS-CoV-2 infection. IMPORTANCE Neutralizing antibody titers are the best correlate of protection against SARS-CoV-2. However, current tests to measure plasma or serum neutralizing activity do not allow high-throughput screening at the population level. Serological tests could be an alternative if they are proved to be good predictors of plasma neutralizing activity. In this study, we analyzed the SARS-CoV-2 serological profiles of two cohorts of health care workers by applying Luminex and ELISA in-house serological assays. Correlations of both serological tests were assessed between them and with a flow cytometry assay to determine plasma surrogate-neutralizing activity. Both assays showed a high positive correlation between IgG levels to S antigens, especially RBD, and the levels of plasma surrogate-neutralizing activity. This result suggests IgG to RBD as a good correlate of plasma surrogate-neutralizing activity and indicates that serology of IgG to RBD could be used to assess levels of protection from SARS-CoV-2 infection.

Anterior Pituitary Hormones in Blood and Cerebrospinal Fluid of Patients in Neurocritical Care.

BACKGROUND: Anterior pituitary hormones in blood follow a circadian rhythm, which may be influenced by various factors such as intracranial pathologies. In cerebrospinal fluid (CSF), pituitary hormones have been collected only selectively and circadian rhythm has not yet been investigated. This pilot study analysed diurnal variations of anterior pituitary hormones in patients in neurocritical care to determine whether circadian rhythmicity exists in these patients. Possible influences of intracranial pathologies were also investigated. Blood and CSF concentrations were assessed simultaneously to explore the value of blood concentrations as a surrogate parameter for CSF levels. METHODS: Blood and CSF samples of 20 non-sedated patients were collected at 06:00, noon, 18:00 and midnight, and analysed for adrenocorticotropic hormone (ACTH), cortisol, thyroid-stimulating hormone (TSH) and insulin-like growth factor-1 (IGF-1) concentrations at each of the four time points. ACTH and IGF-1 were measured by sandwich chemiluminescence immunoassay. Cortisol and TSH were measured by electrochemiluminescence immunoassay. RESULTS: Results showed inconsistent circadian rhythms. Less than 50% of the patients showed a circadian rhythmicity of ACTH, cortisol, TSH or IGF-1. Significance of diurnal variations was only present for blood concentrations of TSH. Correlations between blood and CSF concentrations were strong for cortisol and TSH. CONCLUSIONS: CSF concentrations were only in the measurable range in some of the patients. No clear circadian rhythmicity could be identified, except for TSH in blood. Absence of significant diurnal variations could be explained by the underlying pathologies or disturbing influences of the intensive care unit. Blood concentrations of cortisol and TSH may be suitable surrogate parameters for CSF.

Recruitment of highly cytotoxic CD8+ T cell receptors in mild SARS-CoV-2 infection.

T cell immunity is crucial for control of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and has been studied widely on a quantitative level. However, the quality of responses, in particular of CD8+ T cells, has only been investigated marginally so far. Here, we isolate T cell receptor (TCR) repertoires specific for immunodominant SARS-CoV-2 epitopes restricted to common human Leukocyte antigen (HLA) class I molecules in convalescent individuals. SARS-CoV-2-specific CD8+ T cells are detected up to 12 months after infection. TCR repertoires are diverse, with heterogeneous functional avidity and cytotoxicity toward virus-infected cells, as demonstrated for TCR-engineered T cells. High TCR functionality correlates with gene signatures that, remarkably, could be retrieved for each epitope:HLA combination analyzed. Overall, our data demonstrate that polyclonal and highly functional CD8+ TCRs-classic features of protective immunity-are recruited upon mild SARS-CoV-2 infection, providing tools to assess the quality of and potentially restore functional CD8+ T cell immunity.

Phantosmia, Parosmia, and Dysgeusia Are Prolonged and Late-Onset Symptoms of COVID-19.

Deficiencies in smell and taste are common symptoms of COVID-19. Quantitative losses are well surveyed. This study focuses on qualitative changes such as phantosmia (hallucination of smell), parosmia (alteration of smell), and dysgeusia (alteration of taste) and possible connections with the adaptive immune system. Subjective experience of deficiency in taste and smell was assessed by two different questionnaires after a median of 100 and 244 days after first positive RT-PCR test. SARS-CoV-2-specific antibody levels were measured with the iFlash-SARS-CoV-2 assay. After 100 days a psychophysical screening test for olfactory and gustatory dysfunction was administered. 30 of 44 (68.2%) participants reported a chemosensory dysfunction (14 quantitative, 6 qualitative, 10 quantitative, and qualitative) during COVID-19, eleven (25.0%) participants (1 quantitative, 7 qualitative, 3 quantitative, and quantity) after 100 days, and 14 (31.8%) participants (1 quantitative, 10 qualitative, 3 quantitative and qualitative) after 244 days. Four (9.1%) participants, who were symptom-free after 100 days reported now recently arisen qualitative changes. Serological and T-cell analysis showed no correlation with impairment of taste and smell. In conclusion, qualitative changes can persist for several months and occur as late-onset symptoms months after full recovery from COVID-19-induced quantitative losses in taste and smell.