Detection of IgM antibodies to SARS-CoV-2 nucleocapsid (N) protein, the virus that causes COVID-19, is used in identifying individuals with an adaptive immune response to SARS-CoV-2, indicating recent or prior infection.
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The nucleocapsid protein (N protein) is one of the structural proteins of the SARS-CoV-2 virus. It plays a vital role in packaging the viral RNA genome, making it an essential part of the virus structure. The N protein is located within the virus particle, protecting the viral RNA. Antibodies against the nucleocapsid protein are used in some COVID-19 tests, such as serology tests, to determine whether an individual has been previously exposed to the virus. These tests are not used for early diagnosis but can show if someone has mounted an immune response to the virus, indicating a past infection.
It's important to note that while the presence of antibodies to the nucleocapsid protein can indicate prior exposure to the virus, the duration and level of antibody response may vary among individuals, and it does not necessarily guarantee immunity to future infections.
Antibodies to the spike protein (S) are produced after vaccination.
Antibodies to Nucleocapsid (N) identify individuals who have had a recent or prior COVID-19 infection but are not useful for detecting antibodies elicited by currently available SARS-CoV-2 vaccines.
Coronavirus disease 2019 (COVID-19), is an infectious disease caused by SARS-CoV-2, a virus closely related to the SARS virus. SARS-CoV-2 is the seventh member of the enveloped, positive-stranded RNA viruses that can infect humans. The SARS-CoV-2 genome, like other coronaviruses, encodes for multiple structural and nonstructural proteins. The structural proteins include spike protein (S), envelope protein (E), membrane glycoprotein (M), nucleocapsid phosphoprotein (N), and the nonstructural proteins include open reading frame 1ab (ORF1ab), ORF3a, ORF6, ORF7a, ORF8, and ORF10.
The nucleocapsid (N) protein is the most abundant protein of coronavirus. It is also one of the major structural proteins and is involved in the transcription and replication of viral RNA, packaging of the encapsulated genome into virions, and interference with the cell cycle processes of host cells. Moreover, in many coronaviruses, including SARS-CoV, the N protein has high immunogenic activity and is abundantly expressed during infection.
