Abstract
In December 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel coronavirus (COVID-19), materialized in the city of Wuhan and quickly spread to form a global pandemic. An essential role in the immune system is undertaken by lymphocytes, which defend against bacteria, viruses, fungi, and parasites. Previous study found that very severe COVID-19 patients had suppression of the immune response enabling the virus to spread and cause more damage. This was evident by the changes in their white blood cell and lymphocyte count. Early clinical findings suggest that those suffering from severe COVID-19 have reduced numbers of lymphocytes, monocytes, and other granulocytes. One of the most efficient responses for a variety of viral infections is cellular immune response activation, especially via T cells. Viruses can be eliminated by T cytotoxic (CD8+) (Tc) in the host body, these secrete a variety of molecules, including interferons (IFNs), granzyme, and perforin. T helper (CD4+) (Th) cells help by assisting cytotoxic T cells and B cells to eliminate viral infection. CD8+ and CD4+ work together in a coordinated immune response with other constituents to primarily resolve acute viral infections, and after to produce protection against any reinfection.
 Also, COVID-19 causes dramatic changes in cytokine profiles and serological markers. Therefore, the subsets of immune cells and the level of the pro-inflammatory cytokines are crucial evidence to determine the severity of COVID-19. The disease severity has already been proved to be associated with the disruption in the proinflammatory chemokine response, this eventually leads to a cytokine storm and progression of cytokines release syndrome (CRS). This review aimed to demonstrate a full understanding of the alterations to the immune response by determining the T-cell expression and cytokine levels against the pathological processes of COVID-19, which can be a significant step in early treatment and diagnosis of this disease, in reduction of COVID-19 mortality cases, and to emphasize the most recent and current studies to try to identify new immuno-therapeutics for COVID-19.
Highlights
The end of 2019 witnessed the discovery of a unique coronavirus in Wuhan city, Hubei province, in the Republic of China
This review aimed to demonstrate a full understanding of the alterations to the immune response by determining the Tcell expression and cytokine levels against the pathological processes of COVID-19, which can be a significant step in early treatment and diagnosis of this disease, in reduction of COVID-19 mortality cases, and to emphasize the most recent and current studies to try to identify new immuno-therapeutics for COVID-19
Few coronaviruses have been successful in achieving the cross-species jump and becoming pathogenic to humans; this has been seen in a few outbreaks that have caused significant fatalities during the last 20 years, such as Middle East Respiratory Syndrome Coronavirus (MERS CoV) and severe acute respiratory syndrome coronavirus (SARS-CoV) [6,7]
Summary
The end of 2019 witnessed the discovery of a unique coronavirus in Wuhan city, Hubei province, in the Republic of China This virus soon turned into a global pandemic that affected almost all countries in the world and impacted all aspects of life. One research has found that patients with COVID-19 have elevated liver lactate dehydrogenase (LDH), Creactive protein, and erythrocyte sedimentation rate (ESR) levels [7] Another important observation in severe COVID-19 cases is presence of metabolic acidosis due to elevated levels of lactic acid in the blood, which may be responsible for the inhibition of lymphocyte diffusion [13]. The pathogenesis of COVID-19 is initiated by the binding of the virus to the pulmonary epithelial cells This triggers a chain reaction starting with the immune system, causing an increase in inflammatory mediators such as Interleukin-6 (IL6).
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