Epitope antibody testing is effective in detecting an immune response against SARS-CoV-2

new Preprint * Survey Leaded by Sean SC. Li at Western University in Ontario, Canada, provided evidence of an epitope-specific antibody response and designed a test to measure this in relation to the severity and outcome of post-infection disease.

The authors of the study found that their epitope antibody testing was more useful and effective than traditional screening methods to identify people with plasma and antibodies that were most effective for antibody therapy in the absence of vaccines. It states that there is a possibility.

How they did it

The team created an antibody test by identifying the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen that affects the antibody response.They expressed Spike protein (S), nucleocapsid protein (N), and unstructured protein from ORF1ab gene. Previous studies have suggested that they are the major antigens of the humoral immune response. This created 16 coronavirus proteins and 1 human immunoglobulin G (IgG) as positive controls.

Spike and nucleocapsid proteins are the major antigenic proteins of SARS-CoV-2.

The resulting proteome array was probed with 146 plasma samples taken from 89 patients tested positive or negative for SARS-CoV-2. These patients were divided into two groups based on whether they had severe or moderate coronavirus disease. They were further divided into “living” or “fatal” groups based on whether they survived COVID-19 disease.

A group of patients with moderate or severe illness showed an IgG response to both SARS-CoV-2 peplomer and nucleocapsid proteins, suggesting that they are the major antigens of SARS-CoV-2. Patients admitted to the ICU showed an IgG response specific for spike and nucleocapsid proteins, increased on days 1-7 and 10 in both the survival and fatal groups. This suggests that the humoral response to the S or N protein tends to last longer over time.

The fatal group was likely to show S or N-specific antibodies. Based on the lack of correlation between the strength of the IgG response to S or N and the severity of the disease, researchers found that antibody responses targeting these proteins were either the severity of COVID-19 infection or It suggests that it is not very accurate in predicting the results.

Identification of epitopes of interest in SARS-CoV-2 antibody response

Next, the researchers searched for the exact target of the SARS-CoV-2 antibody reaction. They created peptides with 89 epitopes of S, N, and membrane (M) proteins and exposed them to 14 samples from positive infections and 15 provided plasma samples containing one control. ..

The team found a sharpened antibody response to 54 epitopes from the S and N proteins. To assess the strength of the antibody response to treatment, researchers created a “master epitope array” with 16 epitopes that correspond to strong IgG signaling.

A structural model that shows the location of important epitopes on peplomer proteins. Epitopes S-671, S-811, and S-881 are shown in the domain structure of the spike and its pre-fusion (left) and post-fusion (right) conformations. The S protein has two cleavage sites, S1 / S2 and S2′. The S-671 epitope is located at the C-terminus of S1 and is disordered in the pre-fusion cryo-EM structure (left panel: PDB6XR8). Using the SWISS-MODEL repository homology model, I drew the S671 epitope model in the left panel (blue) without cutting at S1 / S2. The Pro681 site is indicated by a red sphere. The S2’cutting site is at the S-811 epitope. The S-881 epitope is buried and inaccessible in its pre-fusion state. However, this region (fusion peptide or FP) targets the host cell membrane and is completely disordered in the post-fusion conformation (right panel: PDB 6XRA, residues 771-911 are disordered). The S1 area is orange, except for the cyan RBD. The area between the S1 / S2 cut and the S2’cut site is green. The S-811 and S-881 epitopes are magenta in the pre-fusion conformation.

The 16 major epitopes were screened in plasma donated from 89 COVID-19 patients and 9 controls. The findings showed that antibodies from people in the severe ICU group responded to more epitopes than in the moderately infected group.

IgG binding strength was associated with disease severity and outcome. Moderate illness showed a stronger antibody response to N-156, but long-term antibody response to S-811 and S-881 was observed in severe infections.

Researchers have suggested that the active invasion of cells by the coronavirus could lead to the development of S-811 or S-881 epitopes with severe infection and death.

Epitope mutation

The coronavirus peplomer is the most mutated of all coronaviruses and is the reason for the emergence of variants. To better understand this, the team created 28 mutations in the S or N protein. This is related to the B.1.1.7 and B.1351 variants.

The results showed that mutations help reduce or eliminate IgG binding to epitopes. Specifically, the P681H mutation altered the S-671 epitope, making it undetectable by the antibody.

The team has developed a test to measure the epitope antibody response to coronavirus infection. When tested against donated plasma, agglutination was only seen in plasma diagnosed as COVID-19 positive.

Having an S-RBD-dependent antibody response was strongly associated with favorable results. On the other hand, this test found that S-811 (a specific antibody response) was negatively associated with the neutralizing power of patients who recovered from infection. However, S-811 had a positive correlation with severity and mortality. S-RBD-dependent aggregation efficiency was positively associated with neutralization Effectiveness In a living group.

*Important Notices

medRxiv Publish preliminary scientific reports that should not be considered definitive as they are not peer-reviewed, guide clinical practice / health-related behaviors, and should not be treated as established information.