Monocytes and macrophages in COVID-19: Friends and foes

The COVID-19 is a novel infectious disease caused by SARS-CoV-2 and is known as a pandemic emergency that has led to a high rate of mortality throughout the world. Evidence has indicated that hyperinflammatory responses triggered by SARS-CoV-2 are the main cause of pathogenicity in the severe cases of patients who have died during the current viral disease. Monocytes and macrophages as the most important cells of the innate arm of the immune system play a substantial part in the body's defense against viral infections. They mainly respond to the microbial antigens by producing inflammatory mediators to remove pathogens and repair tissue injury. Nevertheless, aberrant alterations in their function such as cytokine storm can be so harmful to the host in the acute respiratory distress syndrome cases caused by SARS-CoV-2. Moreover, inflammatory responses stimulated by SARS-CoV-2 have affected the other vital organs of the body including the heart. As cardiovascular complications in COVID-19 patients have been reported in several studies. During the infection, monocytes and macrophages may be involved in the hypersensitive and exacerbated reactions that contribute to the tissue damage, especially lung injury resulted in its dysfunction and respiratory disorder. In this review, we discuss both advantageous and disadvantageous about the pathological potential of monocytes and macrophages during the infection of SARS-CoV-2 to clarify their mutual effects on immune processing as a fist line defender in the current disease.