The Possible Protective Role of Ghrelin on Acute Stress Induced Thymic Atrophy in Mice. Histological and Immunohistochemical Study

Background: Exposure to stress down regulates the immune system. Thymus gland is sensitive to stress. Ghrelin hormone secreted by the stomach has an immune-stimulatory effect. Aim: Aim of the Work was to study the effect of immobilization stress on mouse thymic population and the possible protective role of Ghrelin. Material and Methods: 40 animals were divided into four groups (10 mice each). Group I was considered as control group. Group II was injected with a 100 μ g/kg of ghrelin intraperitoneally. Group III was immobilized by stress restraint test. Group IV received 100 μ g/kg of ghrelin intraperitoneally prior to the stress restraint test. Thymi of mice of different groups were removed and processed for haematoxylin and eosin, immunohistochemical staining for caspase 3 and electron microscopic studies. Finally, morphometric and statistical analysis were performed. Results: Acute stress resulted in significant decrease in thymic weight. Atrophy of thymic lobules with marked fatty and mononuclear cellular infiltration was detected. Marked decrease in cellularity of thymic cortex was noticed and confirmed by significant increase in caspase 3 positive cells. Medulla showed proliferation of epithelial reticular cells with cystic degeneration in Hassall’s corpuscle. In Ghrelin protected group, the thymus regained normal histological structure with significant decrease in caspase 3 positive cells. Conclusion: Stress resulted in loss of double positive thymocytes to the periphery. Extra thymic T cells were defective, nonfunctional and auto-reactive. Ghrelin allowed activation of surviving thymocytes and prevented apoptosis.