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11BIOLOGICAL SCIENCES
ULTRASTRUCTURAL FEATURES OF THE WHITE THYMUS STROMAL CELLS
Davronova Sh., Kharibova E., Davronov R.
Departments of Human Anatomy, Clinical Anatomy (OHTA) and Histology, Bukhara State Medical Institute, Bukhara, Uzbekistan
Abstract
The ultrastructural features of the stromal cells of the cortical, cortico-medullary and medullary zones of the thymic lobules of white laboratory rats were studied. It was found that in the cortical zone of the thymus lobules of mature rats, dendritic ones are predominantly determined, in the medullary zone, interdigitating and hypertro-phied epithelio-reticulocytes. The cortico-medullary zone is characterized mainly by the presence of monocyte-like cells.
Keywords: immunity, thymus, stromal cells, lymphocytes, receptors.
Relevance of the work: In recent years, in connection with the intensive development of theoretical and applied immunology, the understanding of the structural foundations of immunity has expanded significantly. The cellular and subcellular bases of immunity and the main mechanisms of cooperative interactions of immunocompotent cells - T-, B- lymphocytes and macrophages (A - cells), due to which the body's immune response is provided [1,2,3,4] have been elucidated.
Currently, it is customary to subdivide the organs of immunity into central and peripheral. The central organs of immunity include the thymus gland (thymus) and bone marrow. The peripheral ones include the spleen, lymph nodes, lymphoid formations of the digestive and respiratory tract and the walls of the urinary tract, genital tract. In the central organs of immunity, lymphocytes undergo a series of transformations, as a result of which they acquire the functions of cellular and humoral immunity, enter the peripheral organs, where they participate in the formation of thymus-de-pendent (T-dependent), as well as thymus independent (burs-dependent or B-dependent) structural and functional zones.
It is known that the development and formation of organs of the mammalian immune system, including the thymus, occurs in the embryonic and early postnatal period. In this process, the relationship between the developing organism and the maternal is of decisive importance, if in the antenatal period it is determined by the state of the placenta, then in the early postnatal period the mammary glands [6, 7, 8]. These periods of formation are decisive for the further normal functioning of the immune system in the process of life.
At the same time, until now in the literature there are few works devoted to the features of the ultrastructure of the thymus stromal cells, its various components, which helped to reveal many mechanisms of interstitial and intercellular relationships of the body.
All of the above emphasizes the need to conduct such studies in various mammals.
Purpose of work. Elucidation of morphofunc-tional features of stromal cells of various structural
components of the thymus of white outbred laboratory rats.
Materials and research methods
For the study, we used sexually mature male white laboratory outbred rats, which were kept in accordance with the requirements of the "European Convention for the Protection of Vertebrate Animals used for Experimental and Other Scientific Purposes" (Strasbourg. 1986) and the principles of the Declaration of Helsinki on the humane treatment of animals.
For electron microscopic studies, pieces of thymus were fixed in a 2.5% glutaraldehyde solution at 4 ° C for 40 minutes, followed by additional fixation in a 1% osmic acid solution for 1 hour at 4 ° C. The materials were dehydrated in alcohols of increasing concentration and poured into araldite and epon-812. Ultrathin sections were obtained after taking and corresponding staining of aiming semi-thin sections (E.Enkuzes, F.Erenpreis 1980) on an ultramicrotome from LKB (Sweden). Contrasting was carried out with uranyl acetate and lead citrate, after which the sections were viewed in a JEM-100S electron microscope (JEOL, Japan) of the Department of Histology and Medical Biology of the Tashkent Medical Academy under the guidance of Doctor of Medical Sciences, Professor K.R. Tu-khtaev.
Results of the study: It is known that epitheliore-ticulocytes, which contain class I-II class major histo-compatibility complex molecules on their plasmo-lemma, are important in creating a cellular microenvironment for developing thymocytes (V.I. Pavlenko, I.Yu. Sayapina, 2018).
As our electron microscopic studies have shown, the stromal cells of the thymic lobules of the thymus of white laboratory rats are represented by ordinary stellate epithelioreticulocytes, dentritic and interdigitating cells, as well as cells of macrophage origin - monocyte-like cells and classical macrophages.
Moreover, in the cortical zones, dentritic cells, macrophages and ordinary epithelioreticulocytes are prevalent.
Cortical epithelioreticulocytes are usually stellate. Their intracellular organelles are represented by numerous free ribosomes, polysomes, evenly distributed in
the cytoplasm, and a moderate number of mitochondria. They have few secretory granules, relatively evenly distributed in the cytoplasm.
Along with the classic stellate, spindle-shaped ep-ithelioreticulocytes are found in the cortical zone. These cells contain many tonofibrils, single mitochondria and granular endoplasmic reticulum profiles.
The dendritic cells of the thymus cortex are characterized by the presence of numerous processes, varying in width and length, in contact with a large number of large and medium lymphocytes. They are generally poor in cell organelles, although they contain secretory granules and granular endoplasmic reticulum profiles.
The epithelial cells of the cortico-medullary zone are somewhat different from the cells of the cortical zone. Along with the classic stellate, spindle-shaped epithelioreticulocytes, macrophages, monocyte-like cells and hypertrophied epithelioreticulocytes are found here.
A characteristic feature of hypertrophied cells is the content in the cytoplasm of numerous vacuoles with a groin-like arrangement. The sizes of their vacuoles vary widely - from 0.3 to 4-5 microns in diameter, often take the form of intracellular secretory tubules with short microvilli protruding into the lumen. Cells with a similar ultrastructure were also previously described in the works of K.A. Zufarov, K.R. Tukhtaeva (1987), O.D. Myadel (2016).
Our comprehensive study of the cellular composition of various structural zones of the thymus showed that the number of stromal cells in the medullary zone is 7 times higher than those established for the cortical zone. The age-related nature of the increase in the number of such cells is also described in the works of O.D. Myadel (2018).
The prevailing environments of stromal cells in the medullary zone are interdigitating cells, epithelio-reticulocytes in the Gassalia bodies.
Stromal cells of the cortico-medullary zone are represented mainly by macrophages and monocyte-like cells, the ultrastructure of which practically does not differ from those found in other immune organs and described in numerous works of researchers [3,5].
Based on the ultrastructural studies of thymus stromal cells in white outbred laboratory rats, it can be concluded:
1. The cellular composition of stromal mechano-cytes in various zones of thymic lobules has certain species differences. The most numerous in the cortical zone, along with the usual stellate epithelioreticulocytes, are dendritic cells, macrophages and monocyte-like cells. Interdigitating cells are more concentrated in the medullary zones of the thymic lobules.
2. Macrophages and monocyte-like cells are the predominant component of the cortical and cortico-me-dullary zones of the thymus.
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