Thymic Hormones in Thymus Recovery from Radiation Injury

摘要

The effect of a thymic hormone, thymosin fraction 5 (TF5), in restoring immunocompetence in the thymus of gamma-irradiated mice was examined. Three different mouse strains were used in this study, since previous work has established that the response to TF5 varies in different strains. To measure the rate of recovery of immunocompetent cells in the thymus, the responsiveness to comitogenic effect of interleukn-1 (IL-1) was used. This assay was chosen since it has been established that only more mature PNA, Lytl(+2-) medullary cells respond to this monokine. Contrary to several earlier reports that radio resistant cells repopulating the thymus within the first 10 days after irradiation are mature, corticosteriod resistant, immunocompetent cells, the thymic cells from irradiated mice in all strains used had greatly reduced responses to IL-1. Daily intraperitoneal injections of TF5 increased significantly the responses of thymic cells to IL-1 in 10-13 weeks old C57B1/KsJ, C3H/HeJ, and DBA/1 mice. Older mice, 5 months or more in age, of DBA/1 strain did not respond to treatment with TF5. However, C3H/HeJ mice of the same age were highly responsive. In conclusion, (a) cells repopulating the thymus within 12 days after irradiation contain lower than normal fraction of mature IL-1 responsive cells, (b) thymic hormones increase the rate of recovery of immunocompetent cells in the thymus, and (c) the effect of thymic hormones is strain and age dependent.