Glucocorticoids Impair T Lymphopoiesis after Myocardial Infarction

The thymus, where T lymphocytes develop and mature, is sensitive to insults such as tissue ischemia or injury. The insults can cause thymic atrophy and compromise T cell development, potentially impairing adaptive immunity. The objective of this study was to investigate whether myocardial infarction (MI) induces thymic injury to impair T lymphopoiesis and to uncover the underlying mechanisms. Compared to sham controls, MI mice at day 7 post-MI exhibited smaller thymus, lower cellularity, as well as less thymocytes at different developmental stages, indicative of T lymphopoiesis impairment following MI. Accordingly, the spleen of MI mice has less T cells and recent thymic emigrants (RTEs), implying that the thymus of MI mice releases fewer mature thymocytes than sham controls. Interestingly, the secretory function of splenic T cells was not affected by MI. Further experiments showed that the reduction of thymocytes in MI mice was due to increased thymocyte apoptosis. Removal of adrenal glands by adrenalectomy (ADX) prevented MI-induced thymic injury and dysfunction, whereas corticosterone supplementation in ADX+MI mice reinduced thymic injury and dysfunction, indicating that glucocorticoids mediate thymic damage triggered by MI. Eosinophils play essential roles in thymic regeneration post-irradiation, and eosinophil-deficient mice exhibit impaired thymic recovery after sublethal irradiation. Interestingly, the thymus was fully regenerated in both wild-type and eosinophil-deficient mice at day 14 post-MI, suggesting that eosinophils are not critical for thymus regeneration post-MI. In conclusion, our study demonstrates that MI-induced glucocorticoids trigger thymocyte apoptosis and impair T lymphopoiesis, resulting in less mature thymocyte release to the spleen.