A review on the immune responses against novel emerging coronavirus (SARS-CoV-2)

Abstract

Coronavirus disease 2019 (COVID-19) is a highly contagious disease caused by a newly identified coronavirus called the severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) which was initially emerged in Wuhan, China in late December 2019 and then rapidly extended to other countries worldwide. COVID-19 is now known as a pandemic threat to global public health. It possesses a wide spectrum of clinical manifestations, ranging from asymptomatic infection to mild, moderate, and ultimately severe pneumonia accompanied by multi-organ system dysfunction that can cause the death of the afflicted patients. The host immune system plays a critical role in defending against potentially pathogenic microorganisms such as coronaviruses, and it eliminates and eradicates these invading agents by triggering effective immune responses. However, there exists evidence indicating that in critically ill cases of the COVID-19, dysregulated immune responses and hyper-inflammation lead to acute respiratory distress syndrome (ARDS) and multi-organ failure. Achieving a profound understanding of the pathological immune responses involved in the pathogenesis of COVID-19 will boost our comprehending of disease pathogenesis and its progression toward severe form, contributing to the identification and rational design of effective therapies. In this review, we have tried to summarize the current knowledge regarding the role of immune responses against SARS-CoV-2 and also give a glimpse of the immune evasion strategies of this virus.

Keywords: ACE2; Adaptive immunity; Coronavirus disease 2019; Innate immunity; SARS-CoV-2.

Fig. 1

The viral entry mechanism of SARS-CoV-2 into the host cell (the figure was made with BioRender)

Fig. 2

The immunopathogenesis of COVID-19. The major events implicated in the immunopathogenesis of COVID-19 and the dysregulation of immune response in these patients encompass lymphopenia, increased neutrophil-to-lymphocyte ratio (NLR), cytokine release syndrome (CRS), lymphocyte exhaustion and dysfunction, antibody-dependent enhancement (ADE), and abnormalities of monocytes and granulocytes. It is worth considering that lymphopenia is a key finding in the majority of patients with COVID-19, particularly in those patients with a severe phenotype. PD1, programmed cell death-1; TIM3, T cell immunoglobulin and mucin domain-containing protein-3; NK cell, natural killer cell (the figure was made with BioRender)