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Body response to new Coronavirus (N-Cov-19) and IgM/IgG production

Detection of viral infections currently relies on two major methodologies: Reverse Transcription Quantitative Polymerase Chain Reaction (RT-qPCR) and serological immunoassays that detect viral-specific antibodies (IgM and IgG) or antigens. Rapid IgG/IgM detection provides an easy, cheap, and fast method to find COVID-19 infection but how much is this serological test is reliable?

Coronavirus is a pathogenic viral infection and is highly transmittable. Coronaviruses genomes are enveloped single-stranded RNA, and with a size range of 26-32 kilobases, which is the largest genome of viral RNA. Genotypically coronavirus subfamily is categorized into four groups which are α-alpha, β-beta, ɣ-gamma, and δ-delta. Α-alpha and β-beta coronavirus cause infections in humans.

These viral infections cause upper respiratory tract infections with signs of fever, cough, and headache, and other signs of a  symptom similar to influenza. 

The immune system is the major player when any foreign body enters the human body. The immune system of humans is a complex system protecting against invading bodies. The coronavirus was caused by a new strain of virus SARS-CoV2 in December 2019 which produces pneumonia-like symptoms. The pathophysiology of this virus includes entry into the lungs through respiration. The viral infection initiates the inflammatory responses because of inflammatory chemotactic factors like cytokines (IL-6 and TNF-alpha). These cytokines produce physiological changes including an increase in body temperature resulting in fever. This also causes accumulation of fluid in the lungs and produces difficulty in breathing.

There are 4 types of structural proteins of this novel virus which are S-spike surface glycoprotein, M-matric protein, N-nucleocapsid protein, and E-envelop protein. The S protein act as an adhesion factor to help in getting the entry to the human epithelial cells through the dipeptidyl peptidase-4 receptor. This receptor plays a major role in the activation and initiation of the immune response in the body.

N- protein helps in assembly and virus transcription. Various studies on the response of antibodies IgM and IgG represents the presence of these antibodies in COVID-19 patient after the onset of symptoms. The presence of serum antibodies against the S-protein and N-protein increases within the first 3 weeks of viral infection while S and N- IgM antibodies reach to peak in the second week. In the third week, N and S IgG antibodies continue to rise. The joint antibodies of N and S protein in the first week of infection could detect 75% while its 94.7% in the second week and reach 100% percent detection of antibodies by week 3 of onset of viral infection symptoms.

Variation of the Levels of SARS-CoV-2 RNA and Antigen, IgM and IgG after infection – Source: http://www.diazyme.com/covid-19-antibody-tests

The seThe serum level of N and S IgM antibody decline in few patients because of the IgM and IgG isotype switch that produces more effective antibodies to reduce the replication of the virus. As a response to viral infection, IgM and IgG antibodies are produced as an immune response which serves as a basis for the detection of COVID-19 in suspected patient serum level of N and S IgM antibody decline in few patients because of the IgM and IgG isotype switch that produces more effective antibodies to reduce the replication of the virus. As a response to viral infection, IgM and IgG antibodies are produced as an immune response which serves as a basis for the detection of COVID-19 in suspected patients.

With the rapid spread of COVID-19, there is a rush to develop diagnostic kits for detecting the antibodies produced by the body in response to the viral infection. The testing methodologies rely on the principle of antigen-antibody binding affinity. There are two types of tests, which are immunoassay lab test and cassette-based test. Immune assay detect quantitatively the amount of antibody present the serum while cassette test is impregnated with an antigen which depends on the color change in response to IgM and IgG antibody from the serum.

Although rapid test provides a fast and easy method to detect COVID-19, considering the body response to the new coronavirus and delay in the antibody production, still real-time PCR remains the golden test of COVID-19 detection, at least for the first week of infection.

Clinical Significance of an IgM-IgG Serological Test Result – Source: http://www.diazyme.com/covid-19-antibody-tests

Considering all the above-mentioned points still, IgM/IgG serological assay is a good complement RT-qPCR in the diagnosis of SARS-CoV-2 infections especially for the second screening in the propels who had the previous infection, or they have doubt if they had the previous infection or not!

 

References

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