Determination of IgG Response Profile in SARS-CoV-2 Patients Using a Multiplex Serological Assay

Rapid Communication

Austin J Public Health Epidemiol. 2021; 8(1): 1096.

Determination of IgG Response Profile in SARS-CoV-2 Patients Using a Multiplex Serological Assay

Brochot E1,2*, Souplet V3*, Follet P3, Ponthieu P3, Olivier C3, Even G4, Audebert C4 and Malbec R4

1Department of Virology, Amiens University Medical Center, Amiens, France

2Agents infectieux résistance et chimiothérapie Research Unit, UR4294, Jules Verne University of Picardie, France

3Innobiochips, 70 rue du Dr Yersin, 59120 Loos, France

4GD Biotech, 3595 Route de Tournai, 59501 Douai, France

*Corresponding author: Etienne Brochot, Department of Virology, Amiens University Medical Center, Amiens, France; Agents infectieux résistance et chimiothérapie Research Unit, UR4294, Jules Verne University of Picardie, France

Vianney Souplet, Innobiochips, 70 rue du Dr Yersin, 59120 Loos, France

Received: April 16, 2021; Accepted: May 11, 2021; Published: May 18, 2021


Background: Beyond the diagnosis of SARS-CoV-2 infection, tools delivering a global picture of the patients’ humoral response may be of interest for the comprehension of the disease severity and the assessment of the patients’ protection for vaccination strategy.

Objectives: Here we use a commercial multiplex serological immunoassay CoViDiag®, based on an array of five different antigens of the virus (the Nucleocapsid, the Spike 1 and Spike 2 subunits, and the RBD and NTD domains of the Spike), to investigate the profile of the IgG humoral response for patients with recent SARS-CoV-2 infection depending on the disease severity outcome, or the time post-PCR.

Results: No cross-reaction was observed with the four other seasonal coronaviruses (100% specificity, 0/28). 100% (20/20) of the hospitalized patients PCR-positive to SARS-CoV-2 presented detectable levels of IgGs. 14 days post-PCR diagnosis, 92.3% of the patients, PCR-positive, that did not required hospitalization are presenting IgG (36/39). Interestingly for CoViDiag-positive samples, detectable levels of anti-RBD were found mainly in hospitalized patients (85%, 17/20), while the presence of anti-S1 (60.9%, 28/46) combined with the absence of anti-RBD (6.5%, 3/46) was more characteristic of nonhospitalized patients. Screening campaign group lacked both anti-S1 (18.2%, 4/22) and anti-RBD (4.5%, 1/22).

Conclusion: The CoViDiag® IgG assay could be used to evaluate patients’ immunization and improve their management.

Keywords: SARS-CoV-2; COVID-19; Serological assays; Multiplexing; IgG profile


Since its first detection in Wuhan (China) in December 2019, the Severe Acute Respiratory Syndrome Coronavirus 2 (SARSCoV- 2) has rapidly spread to reach other countries worldwide as the coronavirus 2019 disease (COVID-19) became pandemic [1]. SARSCoV- 2 is spreading through human-to-human contact and can cause respiratory infections among others illness. The clinical picture is very diverse, from asymptomatic infections of healthy carriers, which will increase the disease spreading, to fever, dry cough, breathing difficulties, headache, or pneumonia which make it difficult to differentiate from other respiratory diseases such as flus or human Coronaviruses (hCoVs). Moreover, if most cases are classified as mild (no or moderate signs) in the first stage of the disease, it can rapidly evolve to more severe and critical states and even cause death.

The virions has a nucleocapsid composed by genomic RNA and phosphorylated Nucleocapsid (N) protein, which is buried inside a phospholipid bilayer and covered by the Spike proteins trimmers (S) that gives the CoVs their crown-like appearance on which their names are based. The S protein has two subunits, the Spike 1 (S1) which contains the Receptor-Binding Domain (RBD) and N-Terminal Domain (NTD) and the Spike 2 (S2) [2]. The choice of the antigenic domain is important, as it must be specific to the SARS-CoV-2 for discrimination against other hCoVs for example, and sensitive enough so infection would not be missed [3]. Most commercial serological assays have demonstrated satisfying performances in terms of diagnostic sensitivity and specificity, based on one of those main different antigenic domains [4,5]. It is now generally admitted that severe form of the disease are often associated to excessive immune response and “cytokine storms” [6]. However, kinetics of antibody response and protection efficiency remains poorly understood, especially several months after infection [4,7].


The combination of different antigens could give a more comprehensive picture of the humoral response strength and diversity [8-10]. Thus, this study evaluates the immune profiling performances of the commercial multiplex immunoassay CoViDiag® targeting IgG antibodies against the N, S1, S1-RBD, S1-NTD, and S2 antigens (Figure 1), and its prognosis potential by investigating antibody patterns based on the time post-infection and the disease severity.