Vascular and stromal changes in irradiated and recovering rat thymus

Single cell analysis of complex thymus stromal cell populations: rapid thymic epithelia preparation characterizes radiation injury

Thymic epithelial cells (TECs) and dendritic cells are essential for the maintenance of thymopoiesis. Because these stromal elements define the progenitor niche, provide critical survival signals and growth factors, and direct positive and negative selection, detailed study of these populations is necessary to understand important elements for thymic renewal after cytotoxic injury. Study of TEC is currently hindered by lengthy enzymatic separation techniques with decreased viability. We present a new rapid separation technique that yields consistent viable TEC numbers in a quarter of the prior preparation time. Using this new procedure, we identify changes in stroma populations following total body irradiation (TBI). By flow cytometry, we show that TBI significantly depletes UEA+ medullary TEC, while sparing Ly51+ CD45- cells. Further characterization of the Ly51+ subset reveals enrichment of fibroblasts (CD45- Ly51+ MHCII-), while cortical TECs (CD45- Ly51+ MHCII+) were markedly reduced. Dendritic cells (CD11lc+ CD45+) were also decreased following TBI. These data suggest that cytotoxic preparative regimens may impair thymic renewal by reducing critical populations of cortical and medullary TEC, and that such thymic damage can be assessed by this new rapid separation technique, thereby providing a means of assessing optimal conditioning pretransplantfor enhancing thymic-dependent immune reconstitution posttranspiant.

CCL25 increases thymopoiesis after androgen withdrawal

Although studies have demonstrated that androgen withdrawal increases thymic size, molecular mechanisms underlying this expansion remain largely unknown. We show that decreased androgen signaling leads to enhanced immigration of bone marrow T-cell precursors, as manifested by both an early increase of early thymic progenitors (ETP) and improved uptake of adoptively transferred quantified precursors into congenic castrated hosts. We provide evidence that the ETP niche is enhanced after androgen withdrawal by proliferation of UEA(+) thymic epithelial cells (TEC) and increased TEC production of CCL25, a ligand critical for ETP entry. Moreover, the greatest increase in CCL25 production is by UEA(+) TEC, linking function of this subset with the increase in ETP immigration. Furthermore, blockade of CCL25 abrogated the effects of castration by impairing ETP entry, retarding immature thymocyte development, limiting increase of thymic size, and impairing increase of thymopoiesis. Taken together, these findings describe a cohesive mechanism underlying increased thymic productivity after androgen withdrawal.