Morphological and immunohistochemical characteristics of the thymus of newborns in the early neonatal period

The fetal immune system develops and functions under complex conditions. While it maintains internal fetal homeostasis, it must quickly adapt and respond to maternal antigens. The aim of this study was to examine the pathological and immunohistochemical characteristics of thymus tissue in infants who died in the early neonatal period. The morphological and immunohistochemical characteristics of the thymus were analyzed in 30 infants born to mothers with preeclampsia and eclampsia who died in the early neonatal period. Thymus fragments were obtained at autopsy, fixed in 10 % neutral formalin, and then subjected to standard processing and paraffin embedding. Subsequent histological and immunohistochemical analysis was performed using CD3, CD4, and Ki-67 markers. Statistical analysis of the obtained results was performed using STATISTICA for Windows and MS Excel, employing variation statistics methods. It was established that the statistically significant changes in the integral ratio between the adrenal and thymus masses morphologically indicate the development of premature glucocorticoid-associated thymus involution. Morphologically, a marked increase in the glandular epithelium of the enterochromaffin cells of the zona fasciculata of the adrenal cortex, a sharp increase in the number of lipid inclusions in their cytoplasm, and signs of vascular plethora are noted. The thymus is characterized by a fibrous capsule of variable thickness, a convoluted surface, interstitial edema in the capsule wall, thickening and disorganization of fibrous structures, as well as numerous Hassall's corpuscles and signs of active apoptosis. Morphological changes in the thymus in neonates born to mothers with preeclampsia and eclampsia and those who died in the early neonatal period are accompanied by signs of premature involution and secondary immunodeficiency. High expression of the Ki-67 marker reflects increased proliferative activity of lymphocytes, while low positive expression of CD3+ and CD4+ indicates impaired differentiation of T-lymphocytes and insufficient production of T-helpers, which leads to decreased resistance to infections and the development of immunodeficiency states.

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