University of Guilan Caspian Journal of Environmental Sciences 1735-3033 23 4 2025 10 01 Microstructure of lymphoid tissue in lymph nodes of different localization in young, mature and old rats 979 990 9213 10.22124/cjes.2025.9213 EN Georgii A. Demchenko Laboratory of Physiology Lymphatic System, Institute of Genetics and Physiology SC MSHE RK, 050060 Almaty, Kazakhstan Serik N. Abdreshov Laboratory of Physiology Lymphatic System, Institute of Genetics and Physiology SC MSHE RK, 050060 Almaty, Kazakhstan Zura Yessimsiitova Kazakh National University, al -Farabi, Almaty, Kazakhstan Vladimir Gorchakov Novosibirsk State University, Novosibirsk, Russia Maxat Berdikulov Kazakh National University, al -Farabi, Almaty, Kazakhstan Damir Khussainov Kazakh National University, al -Farabi, Almaty, Kazakhstan Laura Koibasova Laboratory of Physiology Lymphatic System, Institute of Genetics and Physiology SC MSHE RK, 050060 Almaty, Kazakhstan Zhanikha Lessova Kazakh National University, al -Farabi, Almaty, Kazakhstan Journal Article 2025 11 21 Aging is a natural biological process of gradual degradation of parts and systems of the human body and the consequences of this process. These changes occur in the human genotype, both under the influence of environmental factors and as a result of endogenous processes, namely, a deficiency of antioxidant enzymes, changes in the immune system and the development of chronic inflammation. The lymphatic system is the internal environment of the body. In recent years, we and other scientists have determined general and regional signs of aging of the lymphatic system, reflecting a decrease in drainage-detoxification and immune functions, caused by a deficiency of trace elements in the lymph nodes. Considering the important role of the lymphatic system in the body, its participation in tissue drainage and its compensatory and adaptive functions, it is of interest to develop a program of restorative methods of lymphatic system functions on the processes occurring in the aging organism, and thereby contribute to the prolongation of life. This study aimed to determine the ratio of functional zones and microstructures of lymphoid tissue in nodes of different locations in young, mature, and senile rats. Lymph nodes were analyzed using Avtandilov's morphometry, and the samples were fixed in 10% neutral buffered solution formalin or Telesnitsky's fluid, processed, and embedded in paraffin for histological sectioning with various dyes, including hematoxylin and eosin. This study presents data on aging affects the lymph node microstructure and functional area. In young and mature animals, no significant differences were observed. However, aging leads to thickening of the capsule and increased connective tissue around blood vessels, disrupting the lymphoid lobule structure and causing lymph drainage issues. In older animals, the medulla remains unchanged as long as lymph flow is maintained. Compared to younger animals, older ones showed more connective tissue and fewer lymphoid nodules. There is a decreased in certain immune cell types, indicating lower immunoreactivity. Conclusion: In young animals, no significant changes were observed compared to mature animals. Ageing in lymph nodes showed increased connective tissue and reduced lymphoid nodules, with a decrease in certain cell types, and an elevation in the number of reticular cells, indicating lower immunoreactivity. https://cjes.guilan.ac.ir/article_9213_cbaff1006ad1f320b45e9d3b349bee42.pdf