Morphological traits of the thymus of rats in the period of obvious senile changes at immunosuppression caused by administration of cyclophosphamide

Immunosuppressive therapy is necessary in organ transplantation for treatment of autoimmune diseases and malignant tumours. Cytostatic drug cyclophosphamide has many side effects, especially concerning cells with high mitotic activity. Currently, data on the structure of the thymus of laboratory animals at experimental immunosuppression are presented only in a few publications. Moreover, age-related adaptive capability of thymus is still understudied. Objective. The objective of this paper is to study the traits of morphological transformations of the thymus of rats in the period of obvious senile changes at cyclophosphamide administration. Materials and Methods. Thymic microslides were studied using an image analyzer based on CX-41 Olympus microscope. The following parameters were detected in morphofunctional regions of the thymus: percents area of the subcapsular and inner cortical zones; percents area of medulla of thymic lobules, cell arrangement density, percentage of cellular elements: lymphoblasts, small, medium and large lymphocytes, macrophages, mitotically dividing, destructed cells and epithelioreticular cells. Results and Discussion. The decrease of relative area of subcapsular and inner cortical zones in 1-30 days and the increase of this index in the thymic medulla during the whole period of observation after the injection of cyclophosphamide were determined. The density of cells was reduced both in the cortex and medulla. There was a decrease in relative lymphocyte levels, mainly young forms, as well as an increase in the percentage of macrophage and destructed cells. Complete restoration of morphometric characteristics of the thymus in two months after administration of the drug was not detected. Conclusion. The introduction of cyclophosphamide to laboratory animals in the period of obvious senile changes causes the active response of the thymus. In this case, the combination of age (replacement of parenchyma of thymus by adipose tissue, increase of connective tissue structures) and accidental organ involution, manifested by the delymphotization of morphofunctional zones of the thymic parenchyma is observed. Partial restoration of the thymus structure can be noticed only 60 days after cyclophosphamide administration.