SARS-CoV-2 infection: Understanding the immune system abnormalities to get an adequate diagnosis

COVID-19 is a current pandemic that emerged from China at the end of December 2019. Its aetiological agent is the novel coronavirus SARS-CoV-2. To identify biomarkers, diagnostic tools, treatments, or vaccines to decrease COVID-19 incidence and mortality, the scientific community is making extraordinary efforts to understand all aspects of this pathogen, from viral structure to the pathophysiology and immunological processes activated in the host. Diverse abnormalities have been found during SARS-CoV-2 infection both in lymphoid and myeloid cells. Such abnormalities can disturb the immune system function and cause a massive inflammatory response that impairs tissue function. This review discusses the close relationship between immune system abnormalities and the broad spectrum of clinical manifestations, including fibrosis, in the context of COVID-19 disease. Moreover, we have described the current strategies for COVID-19 diagnosis, and we provide a summary of the most useful clinical parameters to identify severe COVID-19 patients.