Author contribution: Guselnikova VV — literature analysis, study planning, staining specimens, analysis and interpretation of the results, manuscript draft writing; Sufieva DA — quantitative data analysis; Tsyba DL — quantitative data analysis; Korzhevskii DE — conceptual development, study planning, manuscript editing.

Compliance with ethical standards: the study was conducted in accordance with the requirements of the World Medical Association Declaration of Helsinki (2013) and approved by the Ethics Committee of the Institute of Experimental Medicine (protocol № 3/18 dated November 22, 2018).