[Morphology of Hassall's corpuscles and their microenvironment in neonates with increased thymus weight].

Objective: To study morphological features of Hassall's corpuscles (HC) and their microenvironment in newborns with increased thymus mass.

Material and methods: The study was carried out on autopsy material of children of the first month of life. Based on the thymic index (TI), 2 groups were identified: with normal (conditional norm) and increased TI value (increased thymus weight). The standard method of histological staining and immunohistochemical methods with antibodies to Pan-CK, CK19, CD68, CD3 and p53 were used in the study. The classification proposed by A.G. Beloveshkin (2013) was used to determine the degree of maturity of HC. Nonparametric Mann-Whitney test was used to determine statistically significant differences in the groups.

Results: In the group of children with increased thymus weight, the number of HC decreased by 20%. It was found that the proportion of progressive and mature corpuscles in this group was reduced by 2.3 and 1.6 times, respectively, compared to the group of children with normal thymus weight, while the proportion of regressive corpuscles increased almost 2-fold. In the HC microenvironment, there is an increase in the total number of thymocytes, combined with a decrease in the expression of CD68, CD3 and p53 in them. A sharp decrease in CK19-expressing cells in this group is accompanied by a disruption in the formation of reticular structures characteristic of the comparison group.

Conclusion: In the thymus with increased mass, the structural and functional organization changes: along with an increase in the total number of thymocytes in the cortical layer and a decrease in the number of macrophages, epithelial cells and HC (with a predominance of regressive corpuscles), disturbances in the processes of maturation, apoptosis and negative selection of lymphocytes occur, which can lead to development of immunogenesis disorders.