Morphofunctional characteristics of blood cells in reconvalescents after suffering COVID-19
Authors: Klyueva S. N. , Kravtsov A. L. , Bugorkova S. A. 
Published: July 2022

Complexity and multifactorial nature of potential pathogenic consequences of SARS-CoV-2 infection in human body, discovery of new virus-induced mechanisms triggering a cascade of pathological responses in the cells of host organism leading to development of multiple organ failure elicited increasing interest in morpho-functional state of blood cells in reconvalescent persons after COVID-19 infection. The aim of the present work is to characterize morphofunctional pattern of blood cells at different periods of recovery, depending on the severity of COVID-19. We examined 55 convalescents after bearing COVID-19 infection: Group I included the convalescents 30 days after the disease (n = 39); Group II consisted of the persons 60 days after recovery (n = 16); Group III included clinically healthy volunteers with no history of clinical SARS-CoV-2 infection (n = 11). The cells were examined by means of Olympus CX41 microscope (Olympus, Japan), and VZ-C31S digital videocamera (VideoZavr, Russia) using the VideoZavr software (version 1.5). Assessment of neutrophil populations in the whole blood samples was performed with BD Accuri C6 Plus flow cytometer (USA) with automatic differentiation of cells between lymphocytes and monocytes, according to the degree of granularity. Cytokine production was determined using commercial kits for detection of IFNγ, TNFα, IL-4, IL-8, IL-10 (JSC Vector-Best, Russia), IL-17A (eBioscience, Austria) was assayed with automatic enzyme immunoassay analyzer “LAZURIT” (Dynex Technologies, USA). Among the convalescents who suffered the moderate-degree COVID-19 (45.5% and 50% of cases, respectively) on days +30 and +60 after clinical recovery, a significantly increased ratio of morphologically altered forms of erythrocytes (echinocytes, ovalocytes, dacryocytes, codocytes) was noted as compared with group III (p = 0.00001 and p = 0.001, respectively). Regardless of clinical severity of the disease; a mean of 40.6% convalescents from groups I and II had moderate disturbances in the neutrophil morphology (cytoplasmic vacuolization, chromatin decondensation at the pre-netosis stage, transformation of cells by the netosis type), and, in 27.4% of cases, the areas of neutrophilplatelet aggregation were seen. In blood supernates from recovered patients, we have revealed a significantly decreased content of IFNγ (P = 0.02), TNFα (p = 0.03), IL-10 (p = 0.04) and IL-17A (p = 0.02). The revealed morphological and functional changes in blood cells in the persons who underwent COVID-19 infection suggest long-term maintenance of toxic damage to erythrocytes, neutrophils and lymphocytes over the recovery period. The effects of the detected morphological and functional disorders of blood cells following COVID-19 recovery leading to increase in blood viscosity and microcirculation, formation of neutrophil-platelet aggregates, may cause higher risks of thrombotic complications at the long-range period as well as decreased levels of regulatory cytokines, thus confirming slow recovery of the lymphocyte populations (Th1, Th2, Th17) of the immune system.