SARS-CoV-2 Multi-Antigen Serology Assay

Proteomics-based mass spectrometry profiling of SARS-CoV-2 infection from human nasopharyngeal samples

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of the on-going global pandemic of coronavirus disease 2019 (COVID-19) that continues to pose a significant threat to public health worldwide. SARS-CoV-2 encodes four structural proteins namely membrane, nucleocapsid, spike, and envelope proteins that play essential roles in viral entry, fusion, and attachment to the host cell. Extensively glycosylated spike protein efficiently binds to the host angiotensin-converting enzyme 2 initiating viral entry and pathogenesis. Reverse transcriptase polymerase chain reaction on nasopharyngeal swab is the preferred method of sample collection and viral detection because it is a rapid, specific, and high-throughput technique. Alternate strategies such as proteomics and glycoproteomics-based mass spectrometry enable a more detailed and holistic view of the viral proteins and host-pathogen interactions and help in detection of potential disease markers. In this review, we highlight the use of mass spectrometry methods to profile the SARS-CoV-2 proteome from clinical nasopharyngeal swab samples. We also highlight the necessity for a comprehensive glycoproteomics mapping of SARS-CoV-2 from biological complex matrices to identify potential COVID-19 markers.

Serological assays to measure dimeric IgA antibodies in SARS-CoV-2 infections

Current serological tests cannot differentiate between total immunoglobulin A (IgA) and dimeric IgA (dIgA) associated with mucosal immunity. Here, we describe two new assays, dIgA-ELISA and dIgA-multiplex bead assay (MBA), that utilize the preferential binding of dIgA to a chimeric form of secretory component, allowing the differentiation between dIgA and monomeric IgA. dIgA responses elicited through severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection were measured in (i) a longitudinal panel, consisting of 74 samples (n = 20 individuals) from hospitalized cases of coronavirus disease 2019 (COVID-19); (ii) a longitudinal panel, consisting of 96 samples (n = 10 individuals) from individuals with mild COVID-19; (iii) a cross-sectional panel with PCR-confirmed SARS-CoV-2 infection with mild COVID-19 (n = 199) and (iv) pre-COVID-19 samples (n = 200). The dIgA-ELISA and dIgA-MBA demonstrated a specificity for dIgA of 99% and 98.5%, respectively. Analysis of dIgA responses in the longitudinal panels revealed that 70% (ELISA) and 50% (MBA) of patients elicited a dIgA response by day 20 after PCR diagnosis with a SARS-CoV-2 infection. Individuals with mild COVID-19 displayed increased levels of dIgA within the first 3 weeks after diagnosis but responses appeared to be short lived, compared with sustained IgA levels. However, in samples from hospitalized patients with COVID-19 we observed high and sustained levels of dIgA, up to 245 days after PCR diagnosis. Our results suggest that severe COVID-19 infections are associated with sustained levels of plasma dIgA compared with mild cases.

A Combined Method Based on the FIPV N Monoclonal Antibody Immunofluorescence Assay and RT-nPCR Method for the Rapid Diagnosis of FIP-Suspected Ascites

Feline infectious peritonitis (FIP), which is caused by feline infectious peritonitis virus (FIPV), is a fatal and immunologically mediated infectious disease among cats. At present, due to the atypical clinical symptoms and clinicopathological changes, the clinical diagnosis of FIP is still difficult. The gold standard method for the differential diagnosis of FIP is immunohistochemistry (IHC) which is time-consuming and requires specialized personnel and equipment. Therefore, a rapid and accurate clinical diagnostic method for FIPV infection is still urgently needed. In this study, based on the etiological investigation of FIPV in parts of southern China, we attempted to explore a new rapid and highly sensitive method for clinical diagnosis. The results of the etiological investigation showed that the N gene of the FIPV BS8 strain had the highest homology with other strains. Based on this, a specific FIPV BS8 N protein monoclonal antibody was successfully prepared by expression of the recombinant proteins, immunization of mice, fusion and selection of hybridoma cell lines, and screening and purification of monoclonal antibodies. Furthermore, we carried out a time-saving combination method including indirect immunofluorescence assay (IFA) and nested reverse transcription polymerase chain reaction (RT-nPCR) to examine FIP-suspected clinical samples. These results were 100% consistent with IHC. The results revealed that the combined method could be a rapid and accurate application in the diagnosis of suspected FIPV infection within 24 hours. In conclusion, the combination of IFA and RT-nPCR was shown to be a fast and reliable method for clinical FIPV diagnosis. This study will provide insight into the exploitation of FIPV N antibodies for the clinical diagnosis of FIP-suspected ascites samples.