Assessment of formation and durability of adaptive immunity in COVID-19 convasescents

Abstract

The study of adaptive immunity in COVID-19 convalescent patients is important, because no consensus on whether the disease severity affects formation and durability of COVID-19 immune response has been achieved. A comparative assessment of emergence and durability of sustained cellular and humoral immunity in convalescent patients with COVID-19 of varying severity was carried out. The study involved volunteers with asymptomatic (n = 30), moderate (n = 21) and severe (n = 12) COVID-19. The average age of the subjects was 47.312.5 years. The formation of cellular immunity was assessed by increased IFN production in response to 1620 hour-long SARS-CoV-2-derived glycoprotein S (RBD) lymphocyte stimulation. To measure IFN level, the Gamma InterferonIFA-BEST test system manufactured by Vector-Best JSC, Russia, was used. The humoral immune response was recorded by detecting SARS-CoV-2RBD-specific class G antibodies using the SARS-CoV-2RBD-ELISA-Gamalei test system (FSBI NITSEM N.F. Gamalei of the Ministry of Health of Russia). It was revealed that humoral and cellular immunity against SARS-CoV-2 proteins was formed in all COVID-19 convalescent patients. However, the number of subjects with adaptive immunity to COVID-19 and the duration of its preservation depends on the severity of the infection. A significant decrease in the number of subjects with cellular immunity was revealed in the group of severe COVID-19. Most of the volunteers in this group had class G immunoglobulins before the end of the follow-up. In this group, unlike the other two, no patients were identified in whom only the cellular arm of the immune response was activated. Volunteers who did not retain adaptive immunity to the COVID-19 pathogen appeared only by the end of the follow-up period. Among those recovered after moderate disease 78 months later there was a decrease in the number of people with cellular and humoral immunity. This process started earlier than in the group of patients who were asymptomatic and continued until the end of the study. The proportion of individuals with cellular immunity increased, and at later timepoint with humoral immune response. By the end of the study, a high percentage of volunteers remained asymptomatically infected, having cellular and humoral immunity to SARS-CoV-2. Their number remained significantly higher than in the group of moderate COVID-19, but lower than in severe COVID-19. By the end of the study, an increased number of volunteers with solely cellular immune response was recorded in this group. At the end of the follow-up period, the number of volunteers with humoral immunity against SARS-CoV-2 remained higher compared to those with a cellular immune response.