Over the past two decades, there have been many publications dealing with the further development of an urgent issue on the immune system of the mucous membranes of the digestive tract, called mucoseassociated lymphoid tissue (MALT), which includes spheres of innate (non-specific) and adaptive (specific) immunity. Most structured formations and indicators of adaptive immunity in the intestinal mucosa are lymphoepithelial formation (Peyer's patches). The data on the formation of the peripheral part of the immune system are carried through the epithelium, mechanisms of interaction between pathogenic intestinal microflora and immunocompetent cells, thereby initiating the development of immune responses in the mucous membranes. A concept has long been established in the literature, according to which a leading role in mediating these reactions belongs to a special type of enterocytes, called M-cells. Before the concept of the initial role of these cells in the development of immune responses in the mucous membranes of the intestinal tract they were known as caveolated cells. The purpose of this study was to determine the shape and topological relations of M-cells with other types of enterocytes, and also with lymphoid elements Peyer's patches of the small intestine. 30 mature albino male rats weighted 200,0±20,0 g were involved into the study. After vivisection, which was carried out by an overdose of thiopental anesthesia (75 mg / kg of animal body weight intramuscularly in the upper third of the thigh of the hind paw) [1] in compliance with the requirements for dissection of the abdominal cavity, the entire complex of the gastrointestinal tract was removed, which was preserved in 10 % formalin solution. Subsequently, short sections of the small intestine, containing Peyer’s patches, were selectively excised. Finding the latter was not difficult due to their clear visualization on the external (nonmesenteric) surface of the small intestine in the form of whitish spots. The specimens, after washing from formalin and dehydration in alcohol of increasing concentration, were embedded into paraffin blocks, from which serial sections of 4 µm thick (Microm HM 325) were obtained with subsequent staining with hematoxylin-eosin and Van Gieson. Their study and documentation was carried out using the “Konus” light microscope equipped with the Sigeta DCM-900 9.0MP digital microphoto attachment and the Biorex 3 program (serial number 5604) adapted for these studies. In the study of many series of paraffin sections stained with hematoxylin-eosin, it was found that while maintaining the general shape of the structure, lymphoid nodules are susceptible to plastic variability, which depends on situationally changing factors of antigenic effect, i.e., functional polymorphism is characteristic of them. This is especially true of their lymphoidassociated epithelium, which appears in a rather diverse form, which depends not only on the section angle, but also, probably, on its reactive state. Thus, in some cases it is a relatively even monolayer of intestinal epithelium, consisting mainly of absorbing enterocytes, among which the most distinct are goblet cells. At the same time, it draws attention to itself that in the apical sections of some of them there are clear signs of rupture of the plasmolemma and the presence in the cytoplasm of basophilic granular fibrous material of an unknown nature. Along with this picture, other histological sections of large lymphoid nodules of Peyer's patches of the small intestine demonstrate a different configurational character of lymphoid-associated epithelium, in which the cluster principle of cell distribution in the form of limited portioned sets is clearly noted. While maintaining the general structural shape, Peyer's patches were found to be subjected to plastic variability, which depends on situationally changing factors of antigenic exposure, i.e., functional polymorphism is characteristic of them. This is especially true of their lymphoid-associated epithelium. Identification of M-cells using only traditional histological methods in practice is complicated. And yet, in the process of a focused study of serial paraffin sections, it was possible to detect some morphological signs indicating their location.
Morphological characteristic of the aggregated lymphoid nodules of the small intestine in the simulation of some factors of space flight
