Abnormal proteolytic activity profile in plasma of blood donors according to anti-SARS-CoV-2 IgG titer

This work aims to study whether there is a relationship between titer values of anti-SARS-CoV-2 IgG and changes in proteolytic processes. To confirm this hypothesis, we analyzed the content and activity of Matrix Metalloproteinases (MMPs) as well as the concentration and composition of circulating peptide pools in the plasma of blood donors divided into groups on the basis of anti-SARS-CoV-2 IgG titers. The results of gelatin zymography showed the presence of active MMP-2 in donors’ plasma who recovered from COVID-19. In contrast, collagenases and their complexes were detected in the plasma of donors with no anti-SARS-CoV-2 IgG, while their activity was undetectable in some groups of COVID-19 convalescent individuals. The content of MMPs also differed among the donors with different titers of anti-SARS-CoV-2 IgG. Plasma peptide content was identical among the donors' groups, but there were more peptide fractions in plasma peptide pools of COVID-19 convalescent individuals; furthermore, they all were characterized by the presence of peptides with molecular weights less than 920 Da and greater than 1530 Da. We hypothesized a link between proteolytic alterations and peptide fraction composition. Our data need further validation to confirm the relationship between the titer values of anti-SARS-CoV-2 IgG and the severity of the proteolytic imbalance.