Poster Presentation 16th Lorne Infection and Immunity 2026

Investigation of microbe associated antibody cross-reactivity in SARS-CoV-2 nucleocapsid immune response (131943)

Joshuah Fialho 1 , Rhiane Moody 1 , Georgia Goodchild 1 , Cyril Deceneux 1 , Monica Prakash 1 , Sabrina Sondah 2 3 , Fay H Johnston 4 5 , Kylie J Smith 4 5 , Nicola Stephens 6 , Michelle McPherson 6 , James H McMahon 7 8 , Ben Rogers 8 9 , Katie Flanagan 2 3 10 , Kirsty Wilson 1 , Magdalena Plebanski 1
  1. School of Health and Biomedical Science, STEM College, RMIT university, Bundoora, VIC, Australia
  2. Tasmanian Vaccine Trial Centre, Clifford Craig Foundation, Launceston General Hospital, Launceston, TAS, Australia
  3. School of Health Sciences and School of Medicine, University of Tasmania, Launceston, TAS, Australia
  4. Public Health Services, Department of Health, Tasmania, TAS, Australia
  5. Menzies Institute for Medical Research, University of Tasmania, Hobart, TAS, Australia
  6. Tasmanian School of Medicine, University of Tasmania, Hobart, TAS, Australia
  7. Department of Infectious Diseases, Alfred Health and School of Translational Medicine, Monash University, Melbourne, VIC, Australia
  8. Monash Infectious Diseases, Monash Health, Clayton, VIC, Australia
  9. Monash University School of Clinical Sciences, Monash Health, Clayton, VIC, Australia
  10. Centre for Infectious Diseases and Microbiology, Westmead Hospital, Westmead, NSW, Australia

While infection with SARS-CoV-2 is characterized by a sequalae of symptoms, an early adaptive immune response is associated with protection. Most of the current immunological research focuses on the spike protein owing to its incorporation in major vaccine formulations. In comparison, studies on the nucleocapsid protein (NP) have been largely limited to serological testing for COVID-19 positivity. However, a prior study from our lab detected anti-nucleocapsid antibodies in SARS-CoV-2 NAT (Nucleic Acid Test) negative health care workers. This suggests potential cross-reactivity could contribute to natural pre-pandemic immunity. We hypothesize that this cross-reactivity could arise from not only genetically similar viruses but also through prior exposure to unrelated microbes. To investigate this, novel NP B-cell epitopes were predicted and run through NCBI BLAST to identify corresponding microbial peptides with similar sequences. This resulted in a total of 10 potential microbial cross-reactive (CR) peptides against 4 NP peptides. Sources of homologous bacterial CR peptides ranged from environmental and human microbiomes to pathogenic species. IgG reactivity to the NP and CR peptides was subsequently evaluated in plasma or sera of COVID-19 negative and convalescent volunteers (n=290), via indirect ELISA. Simultaneous NP and CR peptide recognition was preferentially observed in COVID-19 exposed individuals, indicating a probable boosting of prior immunity to homologous peptides. Donors with dual NP and CR peptide reactivities are being further evaluated for overlapping antibody binding (cross-reactivity), between the NP and CR peptides, via competition ELISA. Initial results suggest the existence of such cross-reactivity and that the regions of similarity or identity within these peptides could be responsible. Thus, the prediction of novel epitopes and delineation of potential cross-reactivity could not only shed light on the breadth of anti-SARS-CoV-2 immunity but also have direct implications for leveraging cross-reactive epitopes to induce protective and sustained immunity via vaccine formulations