Severe COVID-19 alters the biochemical and morphological characteristics of blood cells in a wide variety of ways. To date, however, the vast majority of research has been devoted to the study of leukocytes, while erythrocyte morphological changes have received significantly less attention. The aim of this research was to identify erythrocyte morphology abnormalities that occur in COVID-19, compare the number of different poikilocyte types, and measure erythrocyte sizes to provide data on size dispersion. Red blood cells obtained from 6 control donors (800–2200 cells per donor) and 5 COVID-19 patients (800–1900 cells per patient) were examined using low-voltage scanning electron microscopy. We did not discover any forms of erythrocyte morphology abnormalities that would be specific to COVID-19. Among COVID-19 patients, we observed an increase in the number of acanthocytes (p = 0.01) and a decrease in the number of spherocytes (p = 0.03). In addition, our research demonstrates that COVID-19 causes an increase in the median (p = 0.004) and interquartile range (p = 0.009) when assessing erythrocyte size. The limitation of our study is a small number of participants.

TRNA-derived fragments function as markers in addition to playing the key role of signalling molecules in a number of disorders. It is known that the repertoire of these molecules differs greatly in different cell types and varies depending on the physiological condition. The aim of our research was to compare the pattern of tRF expression in the main blood cell types and to determine how the composition of these molecules changes during COVID-19-induced cytokine storms. Erythrocytes, monocytes, lymphocytes, neutrophils, basophils and eosinophils from control donors and patients with severe COVID-19 were obtained by fluorescence sorting. We extracted RNA from FACS-sorted cells and performed NGS of short RNAs. The composition of tRNA-derived fragments was analysed by applying a semi-custom bioinformatic pipeline. In this study, we assessed the length and type distribution of tRFs and reported the 150 most prevalent tRF sequences across all cell types. Additionally, we demonstrated a significant (p < 0.05, fold change >16) change in the pattern of tRFs in erythrocytes (21 downregulated, 12 upregulated), monocytes (53 downregulated, 38 upregulated) and lymphocytes (49 upregulated) in patients with severe COVID-19. Thus, different blood cell types exhibit a significant variety of tRFs and react to the cytokine storm by dramatically changing their differential expression patterns. We suppose that the observed phenomenon occurs due to the regulation of nucleotide modifications and alterations in activity of various Rnases.

Assessment of viral load levels in various biological samples taken from the respiratory tract can be an indicator of an ongoing process of active viral replication and may be used to monitor severe respiratory viral infections. The study of the relationship between SARS-CoV-2 viral load and immunological laboratory parameters is an important step in the search for clinical markers of COVID-19.The aim of this research was to quantify viral load in patients with COVID-19 and to identify the relation-ship between viral load and changes in the parameters of the cellular component of the immune system.A laboratory examination was carried out on 74 patients diagnosed with COVID-19, they were divided into 3 groups based on the severity of the disease: mild, moderate, severe. Total viral load in clinical samples was determined by the number of SARS-CoV-2 RNA copies per 100 copies of the reference RNaseP gene. A comprehensive assessment of the cellular component of the immune system was performed using flow cytometry and direct monoclonal antibodies, and the IL-6, and C-reactive protein concentrations were determined.We revealed a relationship between the development of serious clinical conditions in the patients with COVID-19, and the levels of viral load. High levels of viral RNA in biological samples correlate with main indicators of the T cell component of the immune system associated with disease severity. In a subgroup of patients with an extremely high viral load, strong positive correlations were found between the relative numbers of cytotoxic lymphocytes (CD3⁺CD8⁺), activated T lymphocytes (CD3⁺HLA-DR⁺), as well as absolute and relative numbers of activated B lymphocytes and NK cells (CD3-CD25⁺).Laboratory monitoring of the cellular component of the immune system, along with the assessment of viral loads, should improve early assessment of clinical condition in the patients with COVID-19. Changes in expression levels of activation markers on immune cells can be potentially viewed as indicators of recovery during COVID-19.

To date, there is no consensus explaining the relationship between varying concentrations of IFNγ and the severity of infection caused by SARS-CoV-2. The aim of this article was to analyze and formulate conclusions from the selected studies and publications, which, in sum, provide a potentially reasonable view on the role of IFNγ in COVID-19 pathogenesis. This article highlights current data on the immunological role of IFNγ which affects differentiation of naive T helper cells, acting as a polarizing factor. It activates the major histocompatibility complex (MHC) class I and II, by increasing the expression of MHC I/II subunits, inhibiting replication of the viral particles by initiating activation of interferon-stimulated genes followed by subsequent synthesis of antiviral proteins. Moreover, IFNγ activates the production of cytokines by T cells, enhancing cytotoxic activity of the T killers. IFNγ exerts immunostimulatory and immunomodulatory effects via STAT1, SOCS1 and PIAS genes, thus regulating activation of the JAK-STAT signaling pathway. A number of studies were considered where the patterns of changes in serum IFNγ concentration were examined in viral infections and SARS-CoV-2. We performed a systemic analysis of the results of studies that showed a relationship between high concentrations of IFNγ and COVID-19 severity. In a number of studies, the significantly high levels of IFNγ in COVID-19 patients were often associated with a poor outcome of the disease. The median values of the IFNγ concentration in severe COVID-19 were found to be significantly higher compared to the results obtained in the cases of moderate severity. It shows an increase, in parallel with viral load in the nasopharyngeal samples upon worsening of the clinical condition. Based on the data on the decreased IFNγ concentrations in convalescent patients, the mechanism of antagonism between IFNγ and IL-4 is considered, where the decreases serum concentrations of IFNγ along with increasing level of IL-4 may be an indirect proof of normal adaptive immune response with subsequent development of antibodies to SARS-CoV-2 and gradual elimination of the virus from the body. Moreover, the evidence is discussed that the patients harboring some parasitic infections (Toxoplasma gondii, Cryptosporidium, Blastocystis hominis, Giardia duodenalis, Entamoeba histolytica) with persistently elevated level of IFNγ are at reduced risk for severe course of COVID-19.

Today, in most cases, the morphology of red blood cells is examined in peripheral blood smears using light microscopy. Computer visualization methods are being implemented everywhere, automated cell counting technologies are being used, and pathological forms of red blood cells are successfully differentiated using neural networks trained on light microscopy images. However, these methods have a certain degree of subjectivity, due to the fact that if the red blood cell does not have a pronounced defect, the operator or the neural network does not always manage to differentiate the various pathological forms. This review article discusses the main methods for assessing the morphology of red blood cells in laboratory practice, describes the characteristics of pathological forms of red blood cells, criteria for their assessment, describes the mechanisms of formation of pathological forms, and considers scanning electron microscopy as an additional method for assessing the morphology.

Severe COVID-19 alters the biochemical and morphological characteristics of blood cells in a wide variety of ways. To date, however, the vast majority of research has been devoted to the study of leukocytes, while erythrocyte morphological changes have received significantly less attention. The purpose of this research was to identify erythrocyte types that were unique to COVID-19, compare the number of different poikilocyte types, and measure erythrocyte sizes to provide data on size dispersion. Red blood cells obtained from 6 control donors (800-2200 cells for each donor) and 5 COVID-19 patients (800-1900 cells for each patient) were examined using low voltage scanning electron microscopy. We did not discover any forms of poikilocytes that would be unique to COVID-19. Among COVID-19 patients, we observed an increase in the number of acanthocytes (p=0.01) and a decrease in the number of spherocytes (p=0.03). In addition, our research demonstrates that COVID-19 causes an increase in the median (p=0.004) and interquartile range (p=0.009) when assessing erythrocyte size.