Systemic and mucosal antibody responses specific to SARS-CoV-2 during mild versus severe COVID-19

Background: Whereas severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific antibody tests are increasingly being used to estimate the prevalence of SARS-CoV-2 infection, the determinants of these antibody responses remain unclear. Objectives: Our aim was to evaluate systemic and mucosal antibody responses toward SARS-CoV-2 in mild versus severe coronavirus disease 2019 (COVID-19) cases. Methods: Using immunoassays specific for SARS-CoV-2 spike proteins, we determined SARS-CoV-2-specific IgA and IgG in sera and mucosal fluids of 2 cohorts, including SARS-CoV-2 PCR-positive patients (n 5 64) and PCR-positive and PCRnegtive health care workers (n 5 109). Results: SARS-CoV-2-specific serum IgA titers in patients with mild COVID-19 were often transiently positive, whereas serum IgG titers remained negative or became positive 12 to 14 days after symptom onset. Conversely, patients with severe COVID19 showed a highly significant increase of SARS-CoV-2-specific serum IgA and IgG titers after symptom onset. Very high titers of SARS-CoV-2-specific serum IgA were correlated with severe acute respiratory distress syndrome. Interestingly, some health care workers with negative SARS-CoV-2-specific serum antibody titers showed SARS-CoV-2-specific IgA in mucosal fluids with virus-neutralizing capacity in some cases. SARSCoV-2-specific IgA titers in nasal fluids were inversely correlated with age. Conclusions: Systemic antibody production against SARS-CoV2 develops mainly in patients with severe COVID-19, with very high IgA titers seen in patients with severe acute respiratory distress syndrome, whereas mild disease may be associated with transient production of SARS-CoV-2-specific antibodies but may stimulate mucosal SARS-CoV-2-specific IgA secretion. (J Allergy

Automated summary

The study found that severe COVID-19 patients experienced a significant increase in SARS-CoV-2 antibody titers after symptom onset, especially with high IgA titers, while mild cases may exhibit transient production of SARS-CoV-2-specific antibodies. Interestingly, some healthcare workers with negative serum antibody titers showed SARS-CoV-2-specific IgA in mucosal fluids with virus-neutralizing capacity in some cases.