CUSABIO’s Human SARS-CoV-2 nucleoprotein (N) IgG Antibody ELISA Kit allows for in vitro qualitative detection of the IgG antibody-specific for SARS-CoV-2 N protein in human serum and plasma. This research-use only kit can be applied in the studies associated with COVID-19, infectious and severe pneumonia caused by SARS-CoV-2. It has been validated with high sensitivity, high specificity, and high precision.
This assay mechanism is based on the qualitative enzyme immunoassay technique. The microtiter plate has been pre-coated with human SARS-CoV-2 nucleoprotein. Samples are pipetted into the wells with anti-human IgG conjugated HRP. Following a thorough wash, the TMB Substrate solution is added to the wells, eliciting a color change. The color develops in proportion to the amount of human SARS-CoV-2 N IgG antibody bound in the initial step. The addition of the stop solution to the wells terminates the color reaction. The color intensity can be measured at 450 nm via a microplate reader. The SARS-CoV-2 N IgG antibody titer in the samples is determined by referring to the negative control. It indicates the presence of SARS-CoV-2 N IgG antibody if the sample O.D. (optical density) is greater than or equal to the cutoff value (2.1×Average O.D. value of negative control). There is no SARS-CoV-2 N IgG antibody present in the sample if the O.D. is less than the cutoff value.
Nucleoprotein is the most abundant protein in SARS-CoV-2. It packs the positive-sense single-stranded viral RNA into a helical ribonucleocapsid (RNP), forming the viral nucleocapsid (N). The N protein plays an important role in improving the efficiency of virus transcription and assembly. It is also involved in viral pathogenesis. N protein possessing an immunogenic effect makes it trigger an immune response, which leads to the production of IgM/G against SARA-CoV-2 N protein. SARS-CoV-2 N IgG antibodies appear in the serum after 2-3 weeks after the onset of the symptoms, peaks within the third week, and gradually declines to a lower level. IgG-specific for SARS-CoV-2 N protein rapidly increases to a higher level after a secondary infection and retains in the body for several months even years.