**Conflict of interest**

*Neutrophils*

**5. Conclusion**

The classical view of the NG, as short-lived finally differentiated cells, which carry out only phagocytosis, killing, and elimination of extracellular pathogens, is convincingly refuted by numerous recent studies. New scientific facts obtained during the last 10–15 years have demonstrated that NGs possess certain regulatory influences of activating, modulating, and suppressive nature, practically on all cells, both innate and adaptive immunity. The development of new diagnostic technologies allowed us to expand and deepen our understanding of the role of the NG in immune homeostasis and to evaluate the dynamic interrelation of the functional potential of the cell with gene expression and phenotypic polarization of the NG in response to inducing signals of intra- and extracellular environment. It is important

CD11b<sup>+</sup>

NG plays an impor-

to note that, to date, not all NG subpopulations have been identified.

tant role in the reactions of phagocytosis and ADCC in infectious processes of various natures. It is also known that CD11b and CD16 NG are the most important triggers inducing the cascade of activation and regulatory processes of the NG. The resting unactivated NGs express the low levels of CD11b and CD16 membrane molecules. After activation additional translocation of intracellular CD16 and CD11b molecules to the NG membrane takes place [6, 36, 63]. Our studies showed that the subpopulation CD16brightCD11bdimNG prevailed in healthy people, and the NG with the phenotype CD16brightCD11bbright was absent in healthy volunteers but appeared and dominated in patients with acute EBV infection. It has been established that CD16brightCD11bdimNG subpopulation predominates in healthy individuals, subpopulation CD16brightCD11bbrightNG prevails in patients with acute viral infection, and CD16dimCD11bbrightNG subpopulation dominates in patients with acute bacterial infection. Identified by us in acute bacterial infection (acute bacterial tonsillitis), emergence of the prevalent population of CD16dimCD11bbright NG indicated, in our opinion, the release into circulation of immature forms of NG in a bacterial attack. At the same time, CD16brightCD11bbright NG subpopulation predominated in patients with acute viral infection (acute EBV infection). We hypothesized that on the one hand, the appearance of CD16brightCD11bbright NG with high cytotoxicity (high levels of CD16 expression) and with a suppressive effect on T-cell proliferation (high levels of CD11b molecules) is necessary for the implementation of antiviral activity of the NG in their fight against EBV infection. CD16brightCD11bbrightNG should have high antiviral activity. On the other hand, their suppressor properties (high levels of CD11b expression) may lead to various complications in the form of secondary bacterial infections. Thus, in severe acute EBV infection, we revealed the transformation of the NG phenotype and the appearance of a new subpopulation of CD16brightCD11bbrightNG with high cytotoxicity and suppressive effects. Further studies are needed to determine the functional significance of the CD16brightCD11bbright NG subpopulation for both EBV infection and other herpesvirus infections. In addition, early diagnosis of the etiological factors that cause an acute infectious process of a viral or bacterial nature is extremely important for the appointment of early etiopathogenetic therapy. The results of the present study demonstrate that the determination of various subpopulations of the NG in the early stages of an acute infectious process can contribute to the early differentiation of an acute viral process in which the CD16brightCD11bbright NG subpopulation dominates and the acute bacterial process dominated by the CD16dimCD11bbright NG subpopulation. On the other hand, it is extremely important to search for new substances that have immunomodulatory effects on the "negatively transformed" phenotype of the NG with the possibility of positive remodeling, which can prevent the attachment of serious complications, both in viral and bacterial infections [63].

Today it is well known that the population of CD16<sup>+</sup>

**54**

Authors declare that there is no conflict of interest.
