J Korean Med Sci.  2023 Sep;38(37):e292. 10.3346/jkms.2023.38.e292.

Clinical Utility of Sero-Immunological Responses Against SARS-CoV-2 Nucleocapsid Protein During Subsequent Prevalence of Wild-Type, Delta Variant, and Omicron Variant

• Lee B
• Ko JH
• Baek JY
• Kim H
• Huh K
• Cho SY
• Kang CI
• Chung DR
• Peck KR
• Kang ES

• KMID: 2546202
• DOI: http://doi.org/10.3346/jkms.2023.38.e292

Abstract

As nucleocapsid protein of severe acute respiratory syndrome coronavirus 2 is immunogenic but not targeted in vaccines, it could be useful in distinguishing natural infection from vaccination. We aimed to investigate the clinical utility of sero-immunological responses against the nucleocapsid protein. Nucleocapsid antibody immunoassay study with 302 coronavirus disease 2019 (COVID-19) patients showed lower titers in immunocompromised patients (P < 0.001), higher titers in higher severity (P = 0.031), and different seroconversion rates and titers according to variants of concern. Longitudinal evaluation of nucleocapsid antibodies using 513 samples from 291 COVID-19 patients revealed that it could persist up to 556 days from symptom onset. Interferon gamma release assay against the nucleocapsid protein showed poor response, precluding the deduction of a cut-off for the nucleocapsid protein. In conclusion, nucleocapsid antibody provides instructive clues about the immunogenicity of nucleocapsid proteins by different seroconversion rates and titers according to the severity of infection, host immune status, and different variants of concern.

Keyword

COVID-19; SARS-CoV-2; Nucleocapsid Proteins; Antibodies; Immunoassay; Interferon-Gamma Release Assay

Figure

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  Fig. 1 Summary of the number of samples used in this study. For each group, two numbers separated with a slash sign (/) were provided where the former and latter numbers indicate the number of samples and individuals, respectively. While only one sample was obtained from each individual in the humoral response analysis, multiple samples from an individual were used in the longitudinal evaluation and the cellular response analysis.COVID-19 = coronavirus disease 2019.

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  Fig. 2 Nucleocapsid antibody test results according to various clinical considerations. Distribution of nucleocapsid antibody results dissected into (A) non-IC (n = 240) and IC patients (n = 62); (B) wild-type (n = 108), delta (n = 40), and omicron (n = 92) samples in non-IC patients; (C) wild-type (n = 4), delta (n = 4), and omicron (n = 54) samples in non-IC patients; (D) mild-to-moderate (n = 164) and severe-to-critical (n = 76) non-IC patients; (E) wild-type (n = 78), delta (n = 8), and omicron (n = 78) samples in mild-to-moderate patients; (F) wild-type (n = 30), delta (n = 32), and omicron (n = 14) samples in severe-to-critical patients; (G) longitudinal evaluation of nucleocapsid antibody titers in 513 samples from 291 coronavirus disease 2019 patients.SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2, COI = cut-off index, IC = immunocompromised, WT = wild-type, Mod = moderate, Crit = critical.

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  Fig. 3 Cell-mediated immune response against SARS-CoV-2 nucleocapsid and spike proteins. (A) Distribution density plot of IFN-γ [N-Nil] results in non-infected healthcare workers (n = 431) and COVID-19 patients (n = 132); (B) IFN-γ results of vaccinees (n = 431); Longitudinal results of (C) IFN-γ [N-Nil] results and (D) IFN-γ [S-Nil] results in patients with SARS-CoV-2 infection (n = 132).ELISA = enzyme-linked immunosorbent assay, IFN = interferon, SARS-CoV-2 = severe acute respiratory distress syndrome coronavirus 2, N = nucleocapsid protein, S = spike protein.

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