Plasma SARS-CoV-2 nucleocapsid antigen levels are associated with lung infection and tissue-damage biomarkers.

BACKGROUND

SARS-CoV-2 nucleocapsid (N) antigen has been confirmed in the peripheral blood of patients with new coronavirus infection,yet its diagnostic and prognostic significance remains unclear. This study aimed to characterize the dynamics of SARS-CoV-2 N antigenemia in patients with novel coronavirus positivity, and to assess its potential association with clinical severity and plasma biomarker levels.

METHODS

We analyzed the level of SARS-CoV-2 N antigen, spike receptor-binding domain (S-RBD) IgG, neutralizing antibodies (NAb) and tissue-damage biomarkers was assessed in 180 plasma samples from 51 SARS-CoV-2-positive individuals. Plasma antigen levels were compared with concurrent respiratory nucleic acid amplification test results.

RESULTS

Patients with Ct values below 30 showed significantly different serum antigen levels compared to those with Ct values above 30 (p < 0.01). However, no significant positive correlation was found between respiratory viral load and serum antigen levels. Further analysis revealed that patients with pneumonia had markedly higher serum antigen levels than those without (p < 0.0001). Additionally, serum amyloid A (SAA) and ferritin (Fe) levels were significantly elevated in the antigenemia-positive group compared to the negative group, while procalcitonin (PCT) and interleukin-6 (IL-6) levels showed no significant differences. Notably, the positivity rate of N antigen in peripheral blood peaked at 47.1% (95% CI: 37.8%-56.7%) during the first week of infection and then gradually decreased over time. Moreover, patients with severe COVID-19 exhibited significantly higher serum antigen levels than those with mild or moderate disease (p < 0.0001). Serum levels of SARS-CoV-2 S-RBD IgG and neutralizing antibodies (NAb) were also significantly higher in antigenemia-negative patients than in antigenemia-positive patients (p < 0.0001).

CONCLUSIONS

Our findings highlight the multifaceted role of antigenemia in SARS-CoV-2 and suggest its potential as a biomarker for disease monitoring and risk stratification.