<p>This retrospective cohort study investigated antigen-specific antibody responses to SARS-CoV-2 and laboratory markers in coronavirus disease 2019 (COVID-19) patients of varying severities. Serum or plasma samples collected early in the pandemic were analyzed for the presence of IgG antibodies and IgG subclasses which target the recombinant spike (S) and nucleocapsid (N) proteins of SARS-CoV-2. Correlation analyses were conducted to assess the possible relationship between the IgG subclasses to SARS-CoV-2 proteins, inflammatory markers, and the severity of the disease. It was shown that the severity of the disease positively correlated with the C-reactive protein (CRP), but most of all with the neutrophil/lymphocyte ratio (NLR) levels. IgG titers against the S- and N-proteins decreased in the most severe COVID-19 cases, which potentially attributed to a delayed IgG formation compared to milder infections. The presence of anti-spike IgG displayed a medium negative correlation trend (not statistically significant, which might be due to the small sample size in our study) with laboratory markers (such as CRP, Fibrinogen, Degree) which are suggestive of infection severity. anti-S IgG correlated positively but weakly with the serum histamine levels. The presence of anti-N IgG at the time of hospitalization correlated with the subsequent outcome. At the same time, anti-N IgG1 correlated with the detection of the viral RNA in the blood. Thus, seroconversion may occur later in patients with a more severe pneumonia. The summary data suggests correlations between the expression of inflammatory markers and the antibody responses, which can also serve as early clinical markers.</p>
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