How does the Immunological System Change during the SARS-COV-2 Attack? A Clue for the New Immunotherapy Discovery.

The COVID-19 pandemic caused by the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-COV-2) is one of the biggest unsolved global problems of the 21st century for which there has been no definitive cure yet. Like other respiratory viruses, SARS-COV-2 triggers the host immunity dramatically, causing dysfunction in the immune system, both innate and adaptive, which is a common feature of COVID-19 patients. Evidence shows that in the early stages of COVID-19, the immune system is suppressed while it is overactive in severe patients characterized by excessive and prolonged inflammatory responses called "Cytokine Storm". There are many elements in the immune system that undergo alterations as the disease progresses. Some significant changes in the innate immune system following infection with SARS-COV-2 include delayed or inhibited interferon type 1 production by the infected cells leading to elevated virus replication, excessive recruitment of activated monocytes and macrophages, decrease in eosinophil population (eosinopenia), consequent decrease in CD8+T lymphocyte proliferation, natural killer (NK) cell dysfunction, and increase in neutrophil infiltration (neutrophilia) and neutrophil extracellular trap (NET) formation. Moreover, hallmark alterations in the adaptive immune system in this process cause an overall decrease in the T lymphocyte number (lymphopenia) and changes in the activity of some lymphocyte subsets and a number of B cells. This review delves into the mentioned changes in the immune system following SARS-COV-2 infection and the implications thereof to guide the development of immunotherapies for patients with COVID-19.