Determination of lymphocyte and cytokine profiles associated with Coronavirus disease 2019 severity

Abstract

Coronavirus disease 2019 (COVID-19) is caused by a recently identified virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the disease is a pandemic. Recurrent waves of infection continue to overwhelm hospitals and claim lives. Severe COVID-19 cases are characterised by an aberrant release of cytokines, lymphopenia and increased neutrophil counts. Although the immunological hallmarks of severe COVID-19 have been established, the underlying mechanisms that promote severe pathology have not been thoroughly studied. A comprehensive understanding of the immune responses observed in severe COVID-19 cases may help guide the development of therapeutic strategies and predict immuno-pathogenicity. This study was set to determine the lymphocyte and cytokine profiles associated with COVID-19 severity. Therefore, a total of 43 hospitalised COVID-19 patients were recruited for the study from Parirenyatwa General Hospital, Harare. Whole blood samples were drawn from each patient within 8 days of admission. Whole blood samples were used to determine the complete blood counts using a haematology analyser and lymphocyte subset populations in each patient using direct immunofluorescence and flow cytometry. A multiplexed cytometric bead array was employed to determine the serum cytokine profiles of each patient. Qualitative analysis of serum C-reactive protein in each patient was also performed and all results were captured and analysed. The demographic characteristics showed that the median age of the patients was 48.72 years, with an interquartile range of 40 to 60 years and 69.77 % of the patients were male. Significant leucocytosis driven by neutrophils and immature granulocytes was observed in COVID-19 patients. Additionally, COVID-19 patients exhibited lower lymphocyte percentages, marked by lower CD4+ counts and percentages. Stratification of patients according to their neutrophil to lymphocyte ratios (NLR) revealed that the high NLR group (NLR > 7.5) had significantly higher immature granulocyte counts and basophil counts. Furthermore, the low NLR group (NLR < 7.5) had significantly higher monocyte counts. There was a prevalent upregulation in interleukin-6 (IL-6) and interleukin-10 (IL-10) expression observed in recruited COVID-19 patients. More importantly, significant incidences of interleukin-17A (IL-17A) expression were observed for the high NLR group. C- reactive protein was demonstrated to be a marker of severe disease. Monocyte percentages were significantly and positively correlated with CD3+, CD4+, CD8+ and CD19+ lymphocytes. According to the results, a systemic neutrophilic environment observed in hospitalised COVID-19 patients may preferentially skew CD4+ lymphocytes towards T-helper 17 and IL-17A promotion, thus, aggravating initial inflammatory responses. A weaker correlation between CD4+ and monocytes than expected indicate a down regulated antigen presenting capacity in COVID-19 patients. Consequently, data from this study strongly suggests broad activity immunomodulation, targeting neutrophils and monoclonal antibodies against IL-17A and IL-6 as therapeutic strategies to treat severe COVID-19 patients.