How COVID-19 Has Globalized: Unknown Origin, Rapid Transmission, and the Immune System Nourishment.

The novel coronavirus disease (COVID-19) profoundly influences T-cell immunity. The counts of total T cells and T-cell subsets, especially CD4+ and CD8+ T cells, are decreased in patients with COVID-19. Also, the function of these cells becomes less effective as the expression of immune inhibitory receptors, such as Tim3 and PD-1, increases over time during the disease. Kinetic analyses show that the T-cell profile changes dynamically, so does the COVID-19 stages. As COVID-19 continues to deteriorate and progresses to severe/critical condition, the lymphocyte count steadily decreases. Therefore, the ability of COVID-19 to escape the immune system might lie in its power to profoundly diminish T-cell effective function, which is necessary for the establishment of a robust antiviral immunity. Also, COVID-19 is associated with increased numbers of monocytes and macrophages, and as the disease progresses from a mild form to a severe/critical condition, the macrophage population becomes denser. Monitoring the expression of cytokines associated with macrophage activation, mainly interleukin (IL)-6 and IL-10, indicates that the course of COVID-19 consists of two stages and the transition between disease stages occurs by the end of the first week after onset of symptoms. At the initial stage, the immune military recognizes the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as nonself and thus fires macrophages at the lungs against the virus. The first flame can control disease progression effectively. However, a trained immunocompetent system would maintain the fire of macrophages over an extended time. It lies in its immune memory in tissue-resident macrophages, especially alveolar macrophages, making a professionally trained immune system more likely to be feared by COVID-19 than an untrained immune system. In this manner, the trained immunocompetent system commits such a failure that causes the lungs to come down rapidly. The fact that younger age groups, including neonates and children, are less susceptible to COVID-19 than older age groups reflects that the natural affinities of the immune system that has not been trained thoroughly would be standard in combatting against COVID-19 whereas the higher affinities of the trained immune system for rapid activation of immune responses might raise faults - the lungs come down.