الفهرس 
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Abstract
Coronavirus disease 2019 (COVID-19) is an emerging viral infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In a few weeks the disease became a global pandemic.
Studies suggested that COVID-19 disease is more severe in individuals with a weakened immune system. Cytotoxic T-cells and NK cells are required to generate an effective immune response against viruses. Patients with severe COVID-19 have significantly lower lymphocyte and higher neutrophil counts in blood. CD8+T lymphocytes and NK cells are significantly reduced in cases of severe infection compared to patients with mild infection and healthy individuals.
NKG2A receptor transduces inhibitory signaling, suppressing T-cell and NK cytokine secretion and cytotoxic function. A recently proposed mechanism via which SARS-CoV-2 overrides innate immune response is by over-expressing NKG2A on CD8+T cells and NK cells, resulting in functional exhaustion of the immune response against the viral pathogen.
This study aimed to assess the expression of NKG2A inhibitory receptor on CD8+T lymphocytes and NK cells in COVID-19 patients and correlate the results with the severity of the disease. This helps to understand the immunological response in COVID-19 infection and consequently the blockade of this receptor by monoclonal antibodies could be a potential therapeutic option.
An observational cross-sectional study was conducted on 30 COVID -19 patients at El Demerdash Geriatrics isolation Hospital.the patients were divided into 2 groups: group I which included 15 moderate cases and group II which included 15 severe cases. A third group which included 10 apparently healthy control was also included in our study. Relevant clinical and demographic data was collected using a standardized data collection form and EDTA anti-coagulated blood samples were obtained for measuring the expression of NKG2A/CD159a on CD56+ NK and CD8+ T cells by flowcytometry using CD159a monoclonal antibodies (Beckman Coulter, USA).
The study revealed lower NK cell percentage and count in COVID19 cases compared to healthy individuals, and the difference between them was statistically highly significant. COVID-19 patients had significantly higher percentage of NK cells expressing NKG2A receptor compared to controls with higher mean fluorescence intensity.
COVID-19 patients also had lower CD8 +T cell count compared to the control group and the difference between them was of high statistical significance. The percentage of CD8 +T cells expressing NKG2A receptor was higher in cases compared to the control group with high statistical significance. Although the mean fluorescence intensity was higher in the COVID-19 patients compared to the control group the difference was not statistically significant.
The results also showed lower NK cell percentage in the group of severe cases compared to moderate ones, but the difference was not statistically significant. NK cell counts were also lower in the group of severe cases and the difference was statistically highly significant. Although the percentage of NK cells expressing NKG2A receptor was higher in group of severe cases compared to the group of moderate cases and the difference was not statistically significant. The mean fluorescence intensity was higher in the severe group with a high statistical significance.
The group of severe cases also had lower CD8 +T cell % but the difference was not statistically significant. However, the CD8 +T cell counts were significantly lower in severe cases. The severe cases had significantly higher percentages of CD8 +T cells expressing NKG2A receptor with higher mean fluorescence intensity.