Studies of altered phagocytic and bactericidal function of neutrophils in patients with post-COVID syndrome, depending on the degree of lung damage detected by computer tomography in acute period of coronavirus infection

By the beginning of May 2023, the epidemic situation regarding COVID-19 was assessed by WHO as favorable, thus enabling to cancel the international emergency state and declare the end of the pandemic on May 5, 2023. Currently, COVID-19 is becoming a seasonal infection. COVID-19 is often accompanied by imbalanced immune response including decreased number of white blood cells and functional changes of immune cells, e.g., affecting activity of neutrophils, including their phagocytic abilities. About 48% of patients who suffered from COVID-19 developed a post-COVID syndrome which is referred to a number of persistent immune disorders which persist for more than 6-12 months after acute infection. Post-COVID-19 disorders of the cellular component of the immune system can manifest with decreased levels of various lymphocyte subpopulations, e.g., NK cells, T cytotoxic lymphocytes, reduced expression of pan-leukocyte CD46 marker on T lymphocytes, as well as changed number and functionality of neutrophils involved in the antiviral immune response. The neutrophils, as a key population of immune system, play an important role in the response to the infection. So far, however, the mechanisms responsible for their functional changes in the context of the post-COVID syndrome remain poorly understood. The results of the study showed that, in patients with post-COVID syndrome, the neutrophil-lymphocyte ratio (NLR) remains within normal range in patients with lung damage of less than 50%. In patients with lung damage of more than 50%, there is a trend for increase of this index, which may suggest a need for in-depth study of immunity in these groups of patients. Statistically significant differences in the innate immunity indexes were detected with respect to phagocytic and bactericidal activity of neutrophils in patients over post-COVID period who showed different extent of lung damage during the acute phase of coronavirus infection.