Cell surface phenotype of cytolytic T lymphocyte precursors in aged nude mice

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Abstract
The cell surface phenotype of cytolytic T lymphocyte precursors (CTL‐P) in congenitally athymic C57BL/6 nu/nu mice has been investigated. CTL‐P were detected and quantitated in a limiting dilution mixed leukocyte microculture assay system supplemented with interleukin 2. Minimal estimates of the frequency of CTL‐P among nylon wool passed (NWP) nude spleen cells were obtained following elimination of Thy‐1‐bearing or Lyt‐2‐bearing cells with monoclonal antibodies plus complement. Alternatively, NWP spleen cells bearing Thy‐1 or Lyt‐2 were positively selected on a cell sorter and assayed for CTL‐P frequency. Both positive and negative selection techniques demonstrated that essentially all (>98%) CTL‐P in NWP nude spleen expressed Thy‐1 and that the majority (80–90%) expressed Lyt‐2. In control NWP spleen cells from normal C57BL/6 mice, > 98% of CTL‐P were positive for both Thy‐1 and Lyt‐2. These data demonstrate that most functional alloreactive CTL‐P developing in the apparent absence of thymic influence already express both Thy‐1 and Lyt‐2 prior to exposure to antigen.