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. 2021 Jan:287:113996.
doi: 10.1016/j.jviromet.2020.113996. Epub 2020 Oct 22.

Anti-SARS-CoV-2 IgG antibody response among Indian COVID-19 patients using β-propiolactone-inactivated, whole virus-based indirect ELISA

Ruta Kulkarni  1 , Harshad P Patil  1 , Sonali Palkar  2 , Sanjay Lalwani  2 , Akhilesh Chandra Mishra  1 , Vidya Arankalle  3
Affiliations

Anti-SARS-CoV-2 IgG antibody response among Indian COVID-19 patients using β-propiolactone-inactivated, whole virus-based indirect ELISA

Ruta Kulkarni et al. J Virol Methods. 2021 Jan.

Abstract

Background: Coronavirus disease 2019 (COVID-19) pandemic caused by infection with severe acute respiratory syndrome - coronavirus-2 (SARS-CoV-2) continues to affect many countries and large populations. Serologic assays for antibody detection aid patient diagnosis and seroepidemiologic investigations.

Methods: An indirect IgG ELISA was developed indigenously using β-propiolactone (BPL) inactivated SARS-CoV-2. This assay was used for screening 200 healthy donor sera collected prior to COVID-19 emergence (2017-2019), 185 serum/plasma samples of confirmed COVID-19 patients (n = 137) and 57 samples of viral RNA positive asymptomatic contacts (n = 51). The IgG response was studied in relation to duration and severity of illness.

Results: The ELISA demonstrated 97 % specificity and IgG detection in >50 %, 80 %, 93.8 % and 100 % of the patients respectively during the first, second, third and fourth week of illness. IgG detection rate was higher in patients with severe disease (SD, 90.9 %) than those with mild disease (MD, 68.8 %) during the second week of illness (P = 0.027). IgG seropositivity among asymptomatic contacts was 64.7 %. IgG ELISA absorbance values were higher in SD than MD patients during the first 2 weeks of illness (P < 0.05). No significant difference was observed between the absorbance values of asymptomatic subjects and MD patients (P = 0.94).

Conclusion: The BPL inactivated virus-based ELISA could detect IgG antibodies early and in a significant proportion of COVID-19 patients suggesting its potential utility as a supplement to the currently used viral RNA detection tests in patient diagnosis and contact screening algorithms.

Keywords: Antibody; COVID-19; ELISA; IgG; Inactivated virus; SARS-CoV-2.

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Conflict of interest statement

The authors report no declarations of interest.

Figures

Fig. 1
Fig. 1
Standardization of inactivated SARS-CoV-2 based indirect IgG ELISA.Fig. 1A shows comparison of different coating antigens (Harvesting at 48 h and inactivation with 0.025 % (A), 0.05 % (B), 0.1 % (C) BPL, harvesting at 72 h and inactivation with 0.025 % (D), 0.05 % (E), 0.1 % (F) BPL) for IgG ELISA, in terms of the ratio of absorbance of positive control to negative control i.e. P/N ratio. Fig. 1B shows comparison of different serum and conjugate dilutions with coating of antigen F at 30,000 PFU/well.
Fig. 2
Fig. 2
Comparison of SARS-CoV-2 IgG detection by in-house ELISA (inactivated whole virus-based) and commercial Euroimmun ELISA (recombinant S1 protein-based). Percent IgG positivity by both the ELISAs among 125 samples is shown – 113 samples collected at different post onset day (POD) of symptoms from COVID-19 patients, 12 samples from asymptomatic subjects.
Fig. 3
Fig. 3
Comparison of IgG ELISA absorbance values for longitudinal samples collected at different post onset day (POD) of symptoms for 22 COVID-19 patients. Blue colour denotes severe disease patients, red colour denotes mild disease patients (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
Fig. 4
Fig. 4
Comparison of IgG ELISA absorbance values for samples collected from patients with mild and severe disease at different post onset day (POD) of symptoms.
See this image and copyright information in PMC

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