Reentry of T cells to the adult thymus is restricted to activated T cells.
To seek information on the capacity of mature T cells to migrate to the thymus, mice were injected with Thy-1-marked populations enriched for resting T cells or T blast cells; localization of the donor cells in the host thymus was assessed by staining cryostat sections of thymus and by FACS analysis of cell suspensions. With injection of purified resting T cells, thymic homing was extremely limited, even with injection of large doses of cells. By contrast, in vivo generated T blast cells migrated to the thymus in substantial numbers. Thymic homing by T blasts was greater than 50-fold more efficient than with resting T cells. Blast cells localized largely in the medulla and remained in the thymus for at least 1 mo post-transfer. Interestingly, localization of T blasts in the thymus was 10-fold higher in irradiated hosts than normal hosts. Thymic homing was especially prominent in mice injected with T blasts incubated in vitro with the DNA precursor, 125I-5-iodo-2'deoxyuridine (125IDUR); with transfer of 125IDUR-labeled blasts to irradiated hosts, up to 5% of the injected counts localized in the host thymus. These data suggest that thymic homing by T blasts might be largely restricted to cells in S phase. The physiological significance of blast cell entry to the thymus is unclear. The possibility that these cells participate in intrathymic tolerance induction is discussed.
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Department of Immunology, Research Institute of Scripps Clinic, La Jolla, California 92037.
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Sprent
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D000818:Animals; D002465:Cell Movement / Q000502:physiology; D004247:DNA / Q000378:metabolism; D007065:Idoxuridine / Q000378:metabolism; D007457:Iodine Radioisotopes; D008198:Lymph Nodes / Q000166:cytology / Q000502:physiology; D008213:Lymphocyte Activation / Q000502:physiology*; D051379:Mice; D016201:Receptors, Lymphocyte Homing / Q000378:metabolism / Q000502:physiology; D016196:S Phase / Q000502:physiology; D013601:T-Lymphocytes / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D013950:Thymus Gland / Q000166:cytology / Q000378:metabolism / Q000502:physiology*
D007457:Iodine Radioisotopes; D016201:Receptors, Lymphocyte Homing; D004247:DNA; D007065:Idoxuridine