Features of humoral immunity after COVID-19

Abstract

At the present time, studying humoral immunity to the new coronavirus infection is among the most important tasks. The COVID-19 infection induces a protective pool of specific antibodies determining severity and duration of such immune protection after convalescence. The antibody testing is also necessary for assessing efficiency of anti-COVID vaccines in order to defeat the SARS-CoV-2 pandemic. Despite enormous interest of scientific community in this problem seen in the literature, there is still a lack for longitudinal observations of immunological status (more than 6 months) in the patients who have undergone COVID-19. The aim of this study is a long-term monitoring (9-14 months) of development and extinction of immune response to SARS-CoV-2 infection using quantitative assessment of IgA and IgG levels in peripheral blood of the patients who had COVID-19 in anamnesis. Monitoring of anti-SARS-CoV-2 levels over time has demonstrated significant individual variability, and made it possible to divide the study participants into three groups, according to characteristic features of humoral immunity after documented COVID-19. The study describes characteristic features of humoral immune response for each of these groups. The first group (30% of the study group) exhibited classical pattern of antibody response to viral infection. The second group (40% of study participants) presented with high plasma IgA levels, and their significant excess (about 2 times) over IgG levels throughout the observation period. The third group (30% of study participants), apparently comprised the subjects with increased humoral immunity to SARS-CoV-2 infection. Their plasma antibodies remain at high levels for at least 9-10 months after the onset of infection. The data obtained confirm the pattern of plasma IgA which is not quite typical to viral infections in dynamics after a sufficiently long time period after the disease in most study participants (2nd and 3rd groups; 70% of all volunteers who have recovered from COVID-19) and suggests an important role of this immunoglobulin against SARS-CoV-2 infection. The specific responses of anti-SARS-CoV-2 IgG are very similar to behavior of such antibodies in other viral infections including contacts with coronaviruses from earlier generations. Humoral immunity against SARS-CoV-2 may persist for more than 6 months, thus supporting an assumption that the naturally infected patients are able to resist re-infection for a long time.