Nucleocapsid Serum Antigen Determination in SARS-CoV-2 Infected Patients Using the Single Molecule Array Technology and Prediction of Disease Severity

Diagnostic Utility of SARS-CoV-2 Nucleocapsid Antigenemia: A Meta-analysis

Background

Studies of the diagnostic performance of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid antigen in blood (antigenemia) have reached variable conclusions. The potential utility of antigenemia measurements as a clinical diagnostic test needs clarification.

Methods

We performed a systematic review of Pubmed, Embase, and Scopus through July 15, 2023, and requested source data from corresponding authors.

Results

Summary sensitivity from 16 studies (4543 cases) sampled at ≤14 days of symptoms was 0.83 (0.75-0.89), and specificity was 0.98 (0.87-1.00) from 6 studies (792 reverse transcription polymerase chain reaction-negative controls). Summary sensitivity and specificity for paired respiratory specimens with cycle threshold values ≤33 were 0.91 (0.85-0.95) and 0.56 (0.39-0.73) from 10 studies (612 individuals). Source data from 1779 cases reveal that >70% have antigenemia 2 weeks following symptom onset, which persists in <10% at 28 days. The available studies suffer from heterogeneity, and Omicron-era data are scarce.

Conclusions

Nucleocapsid antigenemia currently has limited utility due to limitations of existing studies and lack of Omicron-era data. Improved study designs targeting potential clinical uses in screening, surveillance, and complex clinical decision-making-especially in immunocompromised patients-are needed.

Cell surface RNA virus nucleocapsid proteins: a viral strategy for immunosuppression?

Nucleocapsid protein (N), or nucleoprotein (NP) coats the genome of most RNA viruses, protecting and shielding RNA from cytosolic RNAases and innate immune sensors, and plays a key role in virion biogenesis and viral RNA transcription. Often one of the most highly expressed viral gene products, N induces strong antibody (Ab) and T cell responses. N from different viruses is present on the infected cell surface in copy numbers ranging from tens of thousands to millions per cell, and it can be released to bind to uninfected cells. Surface N is targeted by Abs, which can contribute to viral clearance via Fc-mediated cellular cytotoxicity. Surface N can modulate host immunity by sequestering chemokines (CHKs), extending prior findings that surface N interferes with innate and adaptive immunity. In this review, we consider aspects of surface N cell biology and immunology and describe its potential as a target for anti-viral intervention.

Overview of the SARS-CoV-2 nucleocapsid protein

Since the emergence of SARS-CoV in 2003, researchers worldwide have been toiling away at deciphering this virus's biological intricacies. In line with other known coronaviruses, the nucleocapsid (N) protein is an important structural component of SARS-CoV. As a result, much emphasis has been placed on characterizing this protein. Independent research conducted by a variety of laboratories has clearly demonstrated the primary function of this protein, which is to encapsidate the viral genome. Furthermore, various accounts indicate that this particular protein disrupts diverse intracellular pathways. Such observations imply its vital role in regulating the virus as well. The opening segment of this review will expound upon these distinct characteristics succinctly exhibited by the N protein. Additionally, it has been suggested that the N protein possesses diagnostic and vaccine capabilities when dealing with SARS-CoV. In light of this fact, we will be reviewing some recent headway in the use cases for N protein toward clinical purposes within this article's concluding segments. This forward movement pertains to both developments of COVID-19-oriented therapeutic targets as well as diagnostic measures. The strides made by medical researchers offer encouragement, knowing they are heading toward a brighter future combating global pandemic situations such as these.

The role of SARS-CoV-2 nucleocapsid protein in antiviral immunity and vaccine development

ABSTRACTThe coronavirus disease 2019 (COVID-19) has caused enormous health risks and global economic disruption. This disease is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The SARS-CoV-2 nucleocapsid protein is a structural protein involved in viral replication and assembly. There is accumulating evidence indicating that the nucleocapsid protein is multi-functional, playing a key role in the pathogenesis of COVID-19 and antiviral immunity against SARS-CoV-2. Here, we summarize its potential application in the prevention of COVID-19, which is based on its role in inflammation, cell death, antiviral innate immunity, and antiviral adaptive immunity.

Clinical Chemistry and Laboratory Medicine celebrates 60 years – narrative review devoted to the contribution of the journal to the diagnosis of SARS-CoV-2

This review is an integral part of the special issue for the 60 years of the journal Clinical Chemistry and Laboratory Medicine (CCLM). The aim of the review is to highlight the role of the clinical laboratory since the emergence of the “severe acute respiratory syndrome coronavirus 2” (SARS-CoV-2), which causes Coronavirus disease 2019 (COVID-19), with special focus on the contribution of the journal in generating knowledge in SARS-CoV-2 diagnosis. As of October 30, 2022, a total of 186 CCLM publications were dedicated to COVID-19. Of importance, major International Federation of Clinical Chemistry (IFCC) guidelines related to the diagnosis of COVID-19 were published in CCLM. Between early-2020 and late October 2022, COVID-19 publications represented around 27% of all articles in CCLM, highlighting the willingness of the editorial board to help the field in order to better describe and diagnose this new emerging disease. First launched in 1963 under the name “Zeitschrift für Klinische Chemie”, the Journal was entirely devoted to clinical chemistry in the strict sense. The various topics published in relation to COVID-19 including its diagnosis, its impact on biochemical or hematological measures, as well as biosafety measures, is the perfect example that shows that the journal has greatly diversified over time.

Serum SARS-CoV-2 Antigens for the Determination of COVID-19 Severity

The diagnostic of SARS-CoV-2 infection relies on reverse transcriptase polymerase chain reactions (RT-PCRs) performed on nasopharyngeal (NP) swabs. Nevertheless, false-negative results can be obtained with inadequate sampling procedures, making the use of other biological matrices worthy of investigation. This study aims to evaluate the kinetics of serum N antigens in severe and non-severe patients and compare the clinical performance of serum antigenic assays with NP RT-PCR. Ninety patients were included in the study and monitored for several days. Disease severity was determined according to the WHO clinical progression scale. Serum N antigen levels were measured with a chemiluminescent assay (CLIA) and the Single Molecular Array (Simoa) assay. Viremia thresholds for severity were determined and proposed. In severe patients, the peak antigen response was observed 7 days after the onset of symptoms, followed by a decline. No real peak response was observed in non-severe patients. Severity thresholds for the Simoa and the CLIA provided positive likelihood ratios of 30.0 and 10.9 for the timeframe between day 2 and day 14, respectively. Sensitive detection of N antigens in serum may thus provide a valuable new marker for COVID-19 diagnosis and evaluation of disease severity. When assessed during the first 2 weeks since the onset of symptoms, it may help in identifying patients at risk of developing severe COVID-19 to optimize better intensive care utilization.