IMMUNE RESPONSE TO COVID-19 COMPARED TO THE IMMUNE RESPONSE TO SARS, MERS AND INFLUENZA

Abstract

The course, form and outcome of an acute respiratory illness, as well as its patho-histological features largely depend on the level of inflammatory cytokines. The most important proinflammatory cytokines and chemokines are: IL-1α, IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-17A, IFN-γ, TNF-α and GM-CSF. There are many similarities in the human immune response to influenza, SARS and MERS-CoV. Available studies of COVID-19 show a completely different immune response, i.e. immunological indifference or suppression. Influenza is a disease we have known for a long time. WHO has been successfully following the antigenic drift of influenza virus ever since 1952 (WHO’s Global Influenza Surveillance and Response System (GISRS). This is necessary to monitor epidemiological characteristics of influenza as well as for the components of the seasonal vaccine which contains the antigenic characteristics of the subtypes and variants of influenza A virus that circulated in the previous season in the southern hemisphere. Throughout this period, many viruses and bacteria caused respiratory infections, sometimes in increasing epidemic numbers, but it was only the flu that caused serious problems. The epidemics were accompanied by high morbidity and significant mortality. Beta-corona viruses caused a serious warning in 2002 when SARS Cov-1 and MERS in 2012 appeared, followed by high mortality. Alpha corona viruses have been present all this time, but have caused mild upper respiratory infections and rhinitis, without serious consequences. Depending on the season and the region, corona viruses have been present in 10 to 35% of respiratory infections with the immune response to any infectious agent, may be mild, moderate and consequently heal, or severe when due to the high level of cytokines many barriers and membranes can be damaged and cause death. In influenza, the immune response is adequate. Only in a small percentage of cases, an overactive immune response is observed that causes damage and even death. SARS and MERS-CoV have been also shown to elicit a strong immune response. COVID-19 has been present for only a few months, and despite the efforts of many scientists, the epidemiological characteristics and pathogenesis of the disease are still not completely clear. Although COVID-19 belongs to beta corona viruses along with SARS and MERS-CoV, there are differences in the immune response. Whether COVID-19 weakens the immune system, or the immune system does not recognize it as a serious threat, there is a weak immune response during this infection. Such a significant discrepancy in the immune response can help understand the pathogenesis of COVID 19 and the causes of primary viral pneumonia and ARDS followed by high mortality.