Exploring the Immunodominant Epitopes of SARS-CoV-2 Nucleocapsid Protein as Exposure Biomarker

• Published in: Curēus (Palo Alto, CA) Vol. 15; no. 2; p. e34827
• Main Authors: Vashisht, Kapil, Goyal, Bharti, Pasupureddy, Rahul, Na, Byoung-Kuk, Shin, Ho-Joon, Sahu, Dibakar, De, Sajal, Chakraborti, Soumyananda, Pandey, Kailash C
• Format: Journal Article
• Language: English
• Published: United States Cureus Inc 10.02.2023; Cureus
• Subjects: Antibodies; Antigens; Coronaviruses; COVID-19; Genomes; Infectious Disease; Mutation; Pandemics; Patients; Peptides; Poliomyelitis; Proteins; RNA polymerase; Serology; Severe acute respiratory syndrome coronavirus 2; United States > US; Germany; India; covid-19; nucleocapsid protein; protein microarray; sars-cov-2; immunodominant epitopes
• ISSN: 2168-8184; 2168-8184
• DOI: 10.7759/cureus.34827

Background The nucleocapsid protein (N protein) of SARS-CoV-2 is undeniably a potent target for the development of diagnostic tools due to its abundant expression and lower immune evasion pressure compared to spike (S) protein. Methods Blood samples of active COVID-19 infections (n=71) and post-COVID-19 (n=11) were collected from a tertiary care hospital in India; pre-COVID-19 (n=12) sera samples served as controls. Real-time reverse transcriptase-PCR (rRT-PCR) confirmed pooled sera samples (n=5) were used with PEPperCHIP® SARS-CoV-2 Proteome Microarray (PEPperPRINT GmbH, Germany) to screen immunodominant epitopes of SARS-CoV-2. Highly immunodominant epitopes were then commercially synthesized and further validated for their immunoreactivity by dot-blot and ELISA. Results The lowest detectable concentration (LDC) of the N1 peptide in the dot-blot assay was 12.5 µg demonstrating it to be fairly immunoreactive compared to control sera. IgG titers against the contiguous peptide (N2: 156AIVLQLPQGTTLPKGFYAEGS176) was found to be significantly higher (p=0.018) in post-COVID-19 compared to pre-COVID-19 control sera. These results suggested that N2-specific IgG titers buildup over time as expected in post-COVID-19 sera samples, while a non-significant immunoreactivity of the N2 peptide was also observed in active-COVID-19 sera samples. However, there were no significant differences in the total IgG titers between active COVID-19 infections, post-COVID-19 and pre-COVID-19 controls. Conclusion The N2-specific IgG titers in post-COVID-19 samples demonstrated the potential of N protein as an exposure biomarker, particularly in sero-surveillance studies.