Deregulation of endogenous IL-15 alters the T-cell phenotype after allogeneic BMT. Spleens were harvested from syngeneic or allogeneic bone marrow transplant recipients 12 or 13 days after transplantation. (A-B) The percentage of gated CD8⁺ T lymphocytes that were also positive for the activation antigen CD43 was determined by 2-color flow cytometric analysis. Values represent mean ± SE for all groups and are representative of 2 independent experiments involving a total of 17 mice. (C) The percentage of gated lymphocytes that was CD8⁺CD44^highCD62L^low was determined by 3-color flow cytometric analysis. Values represent combined mean ± SE from 3 independent experiments involving a total of 24 mice. (D-E) The ratio of CD4⁺/CD8⁺ T lymphocytes was determined by 2-color flow cytometric analysis. Values represent combined mean ± SE from 3 independent experiments involving a total of 24 mice.