MICRO-FOURIER-TRANSFORM INFRARED REFLECTANCE SPECTROSCOPY AS TOOL FOR PROBING IGG GLYCOSYLATION IN COVID-19 PATIENTS

It has been observed that patients diagnosed with COVID-19 tend to develop severe symptoms primarily during the activation of the adaptive immune response. However, the role of antibodies in the worsening of the disease is not evident. Higher levels of anti-spike IgG1 immunoglobulin, associated with low fucosylation of the antibody's Fc tail, have been linked to an exaggerated inflammatory response. On the other hand, it has also been reported that NP-, S-, and RBD-specific IgA, IgG, and IgM are not correlated with SARS-CoV-2 viral load, suggesting that there is no clear correlation between the antibody response and viral antigen detection. In the present study, micro-Fourier transform infrared reflectance spectroscopy (micro-FTIR) was used to analyze blood serum samples from healthy individuals and people infected with COVID-19 (with mild or oligosymptomatic conditions) (82 healthcare worker volunteers at the “Instituto de Infectologia Emilio Ribas,” São Paulo, Brazil). The quantitative and qualitative FTIR data, sensitive at the molecular level and obtained from 1 µL of dried biofluid, were compared to the signal-to-cutoff index of chemiluminescent immunoassays CLIA and ELISA (IgG antibodies against SARS-CoV-2). Our main finding indicated that the spectral range between 1702–1785 cm⁻¹ (C=O carbonyl vibration) is a spectral marker for the degree of IgG glycosylation, allowing the identification of distinct subpopulations of COVID-19 patients according to disease severity. The specificity was 87.5%, while the true positive detection rate reached 100%. The area under the ROC curve obtained was comparable to CLIA, ELISA, and other ATR-FTIR methods (>0.85). In summary, discrimination between healthy and COVID-19-infected individuals, as well as the prediction of disease severity, could potentially be achieved using micro-FTIR reflectance spectroscopy on blood serum samples. Considering the minimal and reagent-free sample preparation, combined with the rapid (a few minutes) outcome of FTIR, we can conclude that this technology is suitable for fast screening of the immune response in COVID-19 patients. It would be a valuable tool in prospective studies, helping to investigate the physiology of asymptomatic, oligosymptomatic, or severe individuals and to assess the extent of infection spread in patients.