Severe acute respiratory syndrome Coronavirus-2 infection: A synopsis of the host immune responses and viral immune evasion strategies involved

The novel coronavirus designated as SARS-CoV-2 is the etiological agent of coronavirus disease 2019 (COVID-19), which rendered the care of the global health powerless and plunged the world economy into a historic decline. This disease is characterized by different clinical pictures; ranging from asymptomatic mild phase to severe illness with acute respiratory distress syndrome (ARDS), in addition to having no specific therapy. The protective immunity involving solid CD4+ T-cells, viral specific CD8+ T-cells and the neutralizing immunoglobulins have been established in most of the convalescent COVID-19 individuals. On the other hand, the host immune response to severe COVID-19 infection has been attributed to the inflammatory cytokine storm, and to influx of the activated immune cells to the lungs; leading to severe pneumonia, extensive ARDS and finally to death. Despite of this, the protective and pathogenic aspects of the human immunity have not been fully elucidated. Recent attempts conducted by several published research works have focused on information derived from the immune responses to the severe acute respiratory syndrome-related coronavirus diseases (mainly; SARS and MERS). However, these works lack sufficiency due to variations in the transmissibility, virulence, host-virus interactions and the immune evasion mechanisms. Hence, adequate understanding of the host immune response mechanisms to SARS-CoV-2 will generate the impetus towards effective control and preventive measures. The objectives of this article were to provide an overview of the host immune responses to SARS-CoV-2 infection, the viral immune evasion strategies, and to define certain knowledge gaps that require further studies.