Features of rat thymus morphology at the induction of the breast cancer by N-methyl-N-nitrosourea

The immune system as a whole plays a leading role in the formation of an adequate immune response during the onset and development of tumors. The aim of the study was to reveal the features of the change in the morphology and level of biogenic amines of the thymus of rats during experimental carcinogenesis of breast cancer by the injection of N-methyl-N-nitrosourea. In the work used luminescence-histochemical, general histological and immunohistochemical methods, which made it possible to obtain important information about the functional activity of the cellular elements of the thymus, the quantitative composition of macrophages, dendritic cells, lymphocytes and the qualitative characteristics of mast cells. The experiment was carried out on 85 white nonlinear female rats, which were injected with the carcinogen N-methyl-N-nitrosourea, which induces a breast tumor. Animals were divided into two groups: intact (n=30) and rats injected with a carcinogen (n=45). The thymus structure was examined 1, 2, and 3 months after the end of the injections. During the study, changes in the morphometric parameters of the organ are noted. A month after the injection of the drug, the area of the medulla of the thymus and the thickness of the cortex substance of the organ increases, which decrease with an increase in the study period. Replacement of the thymus parenchyma with adipose and connective tissue begins after 2 months and progresses with an increase in the study period. A tendency to wavelike changes in biogenic amines was revealed, after 1 month there is a significant increase in the level of histamine and a decrease in serotonin and catecholamines, after 2 months an increase in all biogenic amines, especially histamine (1.5 times or more) in premedullary and mast cells, thymocytes of the cortex. After 3 months, on the contrary, there is a decrease in histamine and an increase in the level of monoamines. The ratio (serotonin+histamine)/catecholamines after 1 month indicate a decrease in the functional activity of the thymus, and after 3 months - about its increase. At all stages of the study, degranulated forms of mast cells predominate. In the dynamics of the experiment, an increase in the number of dendritic cells, lymphocytes, and twice the number of macrophages and Bcl-2+cells was revealed. The data obtained in the course of the study suggested that the introduction of N-methyl-N-nitrosourea and the subsequent development of a breast tumor is reflected in the change in the morphofunctional state of the thymus. In this case, the greatest changes were observed 2 months after the end of the administration of the carcinogen, even before the formation of a breast tumor. The data obtained can have a certain value in determining the immune status in models of experimental carcinogenesis.