Role of macrophages and monocytes in SARS-CoV-2 infection and in severe COVID-19 course

Abstract

In this review, I describe in an accessible manner how macrophages are involved in both the body's defense against SARS-CoV-2 infection and COVID-19, and how they can contribute to the severe course of this disease. Macrophages constitute the body's first line of defense against the ingress of viruses, including the SARS-CoV-2 coronavirus. Among other actions, they cause inflammation that allows the consolidation of the entire immune system in COVID-19. However, macrophages become also infected with the coronavirus, and in consequence they secrete too much cytokines and lose their ability to extinguish the inflammation. By acting on the ACh α4/α7 nicotinic receptors (nAChR), nicotine may attenuate the pro-inflammatory effects of SARS-CoV-2 infected macrophages and reduce the cytokine storm induced by them in the lungs. Monocytes, which are the precursor cells of macrophages and of at least some tissue macrophages, can carry SARS-CoV-2 in patients to organs such as pancreas, testes and epididymis and induce an inflammatory process that can cause diabetes, orchitis or epididymitis.